Sunscreen (also known as sunblock, suntan lotion) is a lotion, spray or other topical product that helps protect the skin from the sun's ultraviolet (UV) radiation, and which reduces sunburn and other skin damage, ultimately leading to a lower risk of skin cancer However, suntan lotion is an incorrect term for sunscreen as it is something entirely different Suntan lotion is used to moisturize and maximize UV exposure and tanning, rather than block it These are commonly called indoor tanning lotions when designed for use with tanning beds or just suntan lotion if designed for outdoor use and may or may not have SPF protection in them
The best sunscreens protect against both UVB (ultraviolet radiation with wavelength between 290 and 320 nanometres), which can cause sunburn, and UVA (between 320 and 400 nanometres), which damages the skin with more long-term effects, such as premature skin aging Most sunscreens work by containing either an organic chemical compound that absorbs ultraviolet light (such as oxybenzone) or an opaque material that reflects light (such as titanium dioxide, zinc oxide), or a combination of both Typically, absorptive materials are referred to as chemical blocks, whereas opaque materials are mineral or physical blocks
Dosing for sunscreen can be calculated using the formula for body surface area and subsequently subtracting the area covered by clothing that provides effective UV protection The dose used in FDA sunscreen testing is 2 mg/cm²[1] Provided one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32 in (82 cm) waist, that adult wearing a bathing suit covering the groin area should apply 29 g (approximately 1 oz) evenly to the uncovered body area Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face
Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, research has shown that the best protection is achieved by application 15–30 minutes before exposure, followed by one reapplication 15–30 minutes after the sun exposure begins Further reapplication is only necessary after activities such as swimming, sweating, and rubbing[2]
However, more recent research at the University of California indicates that sunscreen needs to be reapplied within 2 hours in order to remain effective Not reapplying could even cause more cell damage than not using sunscreen at all, due to the release of extra free radicals from absorbed chemicals[3]
Dosing for sunscreen can be calculated using the formula for body surface area and subsequently subtracting the area covered by clothing that provides effective UV protection The dose used in FDA sunscreen testing is 2 mg/cm²[1] Provided one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32 in (82 cm) waist, that adult wearing a bathing suit covering the groin area should apply 29 g (approximately 1 oz) evenly to the uncovered body area Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face
Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, research has shown that the best protection is achieved by application 15–30 minutes before exposure, followed by one reapplication 15–30 minutes after the sun exposure begins Further reapplication is only necessary after activities such as swimming, sweating, and rubbing[2]
However, more recent research at the University of California indicates that sunscreen needs to be reapplied within 2 hours in order to remain effective Not reapplying could even cause more cell damage than not using sunscreen at all, due to the release of extra free radicals from absorbed chemicals[3]
Dosing for sunscreen can be calculated using the formula for body surface area and subsequently subtracting the area covered by clothing that provides effective UV protection The dose used in FDA sunscreen testing is 2 mg/cm²[1] Provided one assumes an "average" adult build of height 5 ft 4 in (163 cm) and weight 150 lb (68 kg) with a 32 in (82 cm) waist, that adult wearing a bathing suit covering the groin area should apply 29 g (approximately 1 oz) evenly to the uncovered body area Considering only the face, this translates to about 1/4 to 1/3 of a teaspoon for the average adult face
Contrary to the common advice that sunscreen should be reapplied every 2–3 hours, research has shown that the best protection is achieved by application 15–30 minutes before exposure, followed by one reapplication 15–30 minutes after the sun exposure begins Further reapplication is only necessary after activities such as swimming, sweating, and rubbing[2]
However, more recent research at the University of California indicates that sunscreen needs to be reapplied within 2 hours in order to remain effective Not reapplying could even cause more cell damage than not using sunscreen at all, due to the release of extra free radicals from absorbed chemicals[3]
The principal ingredients in sunscreens are usually aromatic molecules conjugated with carbonyl groups This general structure allows the molecule to absorb high-energy ultraviolet rays and release the energy as lower-energy rays, thereby preventing the skin-damaging ultraviolet rays from reaching the skin So, upon exposure to UV light, most of the ingredients (with the notable exception of avobenzone) do not undergo significant chemical change, allowing these ingredients to retain the UV-absorbing potency without significant photo-degradation[1]
当我们使用 "more than" 时，通常是想要表达某个数量、程度、比例或其他方面的超过某个特定的阈值：
1 表示数量或程度超过某个特定的数值或水平
当我们想要表达某个数量或程度超过某个特定的数值或水平时，通常使用 "more than"。例如：
- "The temperature today is more than 30 degrees Celsius"（今天的温度超过30摄氏度。）
- "She has been working for more than 10 hours today"（她今天已经工作了10个小时以上。）
- "The car can go more than 100 kilometers per hour"（这辆车可以以每小时100公里以上的速度行驶。）
2 表示某物的数量或程度比其他事物更多或更大
"more than" 还可以用来表示某物的数量或程度比其他事物更多或更大。例如：
- "This supermarket has more than 10 checkout counters"（这家超市有10个以上的收银台。）
- "The United States has more than 50 states"（美国有50个以上的州。）
- "He has more than enough money to buy a new car"（他有足够多的钱买一辆新车。）
3 表示某事情比预期或期望的更多或更大
"more than" 还可以用来表示某事情比预期或期望的更多或更大。例如：
- "More than 1,000 people attended the rally"（有1,000人以上参加了集会。）
- "The project will take more than a year to complete"（这个项目需要一年以上才能完成。）
- "The movie made more than $100 million at the box office"（这部**在票房上的收入超过1亿美元。）
4 表示一种情感的强烈程度
"more than" 还可以用来表示一种情感的强烈程度。例如：
- "I am more than happy to help you"（我非常高兴能帮助你。）
- "She is more than excited about the new job"（她对新工作非常兴奋。）
- "He is more than willing to go on the trip"（他非常愿意去旅行。）
5 表示一种比较的程度
最后，"more than" 还可以用来表示一种比较的程度。例如：
- "She is more than just a friend to me"（她对我来说不仅仅是个朋友。）
- "This is more than a hobby for him; it's his passion"（对他来说，这不仅仅是一种爱好，而是他的激情。）
需要注意的是，“more than”也可以用于表示程度的相反面，即表示相对少或不足。例如：
- "She has more than enough money to buy a new car"（她有足够多的钱买一辆新车。）
- "I have more than half a cake left"（我还有一半多的蛋糕。）
知识点拓展：
"more than" 与 "over" 与 "above" 都有类似的意思，都表示某个数量或程度超过某个特定的阈值。但是它们的使用上有一些区别。 "over" 通常用于描述数值或程度的增长，如 "The price of the stock went up over 10%"（股票价格上涨了超过10%）。 "above" 通常用于描述物体的位置或数量，如 "The airplane is flying above the clouds"（飞机在云层上方飞行）。在大多数情况下，"more than" 可以与 "over" 和 "above" 互换使用，但在一些语境下，它们的用法略有不同。
此外，在正式的写作中，"more than" 和 "over" 的使用可能会受到不同的限制。例如，在某些学术论文中，要求使用“more than”而不是“over”，因为"over"可能被认为太口语化。在某些商业写作中，也可能会避免使用 "more than"，而使用 "in excess of" 或 "greater than" 这样更正式的词语。
more可以作为many或者much的比较级，直接接名词，如more coffee，more books
另外，more也是构成形容词比较级中的一个结构。对于多音节的形容词的比较级，我们要加more，如beautiful一次，比较级是more beautiful，而普通的单音节的形容词，就像poor，rich，比较级是poorer ，richer。
英语语法---比较级和最高级的用法
在英语中通常用下列方式表示的词:在形容词或副词前加more(如 more natural,more clearly )或加后缀 -er(newer,sooner )典型的是指形容词或副词所表示的质、量或关系的增加英语句子中,将比较两个主体的方法叫做“比较句型”其中,像“A比B更……”的表达方式称为比较级；而“A最……”的表达方式则称为最高级组成句子的方式是将形容词或副词变化成比较级或最高级的形态
一、形容词、副词的比较级和最高级的构成规则
1．一般单音节词和少数以-er,-ow结尾的双音节词,比较级在后面加-er,最高级在后面加-est；
（1）单音节词
如：small→smaller→smallest short→shorter→shortest
tall→taller→tallest great→greater→greatest
（2）双音节词
如：clever→cleverer→cleverest narrow→narrower→narrowest
2．以不发音e结尾的单音节词,比较在原级后加-r,最高级在原级后加-st；
如：large→larger→largest nice→nicer→nicest able→abler→ablest
3．在重读闭音节（即：辅音＋元音＋辅音）中,先双写末尾的辅音字母,比较级加-er,最高级加-est；
如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest
4．以“辅音字母＋y”结尾的双音节词, 把y改为i,比较级加-er,最高级加-est；
如：easy→easier→easiest heavy→heavier→heaviest
busy→busier→busiest happy→happier→happiest
5．其他双音节词和多音节词,比较级在前面加more,最高级在前面加most；
如：beautiful→more beautiful→most beautiful
different→more different→most different
easily→more easily→most easily
注意：（1）形容词最高级前通常必须用定冠词 the,副词最高级前可不用
例句： The Sahara is the biggest desert in the world
（2） 形容词most前面没有the,不表示最高级的含义,只表示"非常"
It is a most important problem
=It is a very important problem
6．有少数形容词、副词的比较级和最高级是不规则的,必须熟记
如：good→better→best well→better→best
bad→worse→worst ill→worse→worst
old→older/elder→oldest/eldest
many/much→more→most little→less→least
far →further/farther→ furthest/farthest
二、形容词、副词的比较级和最高级的用法
1．“A + be +形容词比较级 + than + B” 意思为“A比B更……”
如：This tree is taller than that one 这棵树比那棵树高
注意：
① 在含有连词than的比较级中,前后的比较对象必须是同一范畴,即同类事物之间的比较
②在比较级前面使用much,表示程度程度“强得多”
如：A watermelon is much bigger than an apple
③ very, quite一般只能修饰原级,不能修饰比较级
2．“比较级 + and + 比较级”或“more and more +原级”表示“越来越……”
如：It becomes warmer and warmer when spring comes
春天来了,天气变得越来越暖和了
It is getting cooler and cooler
天气越来越凉爽
The wind became more and more heavily
风变得越来越大
Our school is becoming more and more beautiful
我们的学校变得越来越美丽
3．在含有or的选择疑问句中,如果有两者供选择,前面的形容词要用比较级形式
如：Who is taller,Tim or Tom 谁更高,Tim还是Tom
4 “the +比较级……, the+比较级”,表示“越……越……”
The more money you make, the more you spend
钱你赚得越多,花得越多
The sooner,the better
越快越好
5 表示倍数的比较级用法：
① A is …times the size /height/length/width of B
如：The new building is three times the height of the old one
这座新楼比那座旧楼高三倍(新楼是旧楼的四倍高)
② A is …times as big /high/long/wide/large as B
如：Asia is four times as large as Europe
亚洲是欧洲的四倍大(亚洲比欧洲大三倍)
③ A is …times larger /higher/longer/wider than B
如：Our school is twice bigger than yours
我们学校比你们学校大两倍
6形容词、副词的最高级形式主要用来表示三者或三者以上人或事物的比较,表示“最……”的意思
句子中有表示范围的词或短语如：of the three, in our class等等
如：He is the tallest in our class
他在我们班里是最高的
7"否定词语+比较级","否定词语+ so… as"结构表示最高级含义
Nothing is so easy as this
=Nothing is easier than this
=This is the easiest thing
8 比较级与最高级的转换：
Mike is the most intelligent in his class
Mike is more intelligent than any other student in his class
7修饰比较级和最高级的词
1）可修饰比较级的词
①a bit, a little, rather, much, far, by far, many, a lot, lots, a great deal, any, still, even等
② 还可以用表示倍数的词或度量名词作修饰语
③ 以上词(除by far)外,必须置于比较级形容词或副词的前面
注意： 使用最高级要注意将主语包括在比较范围内
(错) Tom is the tallest of his three brothers
(对) Tom is the tallest of the three brothers
2)下列词可修饰最高级：by far, far, much, mostly, almost
This hat is nearly / almost the biggest
注意：
a very可修饰最高级,但位置与much不同
This is the very best
This is much the best
b 序数词通常只修饰最高级
Africa is the second largest continent
8要避免重复使用比较级
(错) He is more cleverer than his brother
(对) He is more clever than his brother
(对) He is cleverer than his brother
9要避免将主语含在比较对象中
(错) China is larger that any country in Asia
(对) China is larger than any other country in Asia
10要注意对应句型,遵循前后一致的原则
The population of Shanghai is larger than that of Beijing
It is easier to make a plan than to carry it out
11要注意冠词的使用,后有名词的时候,前面才有可能有名词
比较：Which is larger, Canada or Australia
Which is the larger country, Canada or Australia
She is taller than her two sisters
She is the taller of the two sisters
三典型例题
1） ---- Are you feeling ____
---- Yes,I'm fine now
A any well B any better C quite good
D quite better
答案：B any 可修饰比较级,quite修饰原级,well的比较级为better
2）The experiment was____ easier than we had expected
A more B much more C much
D more much
答案：C much可修饰比较级,因此B,C都说得通,但easier本身已是比较级,不需more,因此C为正确答案
3）If there were no examinations, we should have ___ at school
A the happiest time B a more happier time
C much happiest time D a much happier time
答案：D
比较级和最高级的用法
1两者相比（甲=乙）,用“as+原级+as”表示
Tom is as tall as Mike
2两者相比（甲〈 乙）,用“not as(so) +原级+as”或“less than”表示
I didn’t do my homework so(as) carefully as you
The picture is less attractive than that one
3两者相比（甲〉乙）,用“比较级+than”表示
Our city is more beautiful than any other city in our country
注意：1) 为了避免重复,在从句中常用one, that, those等词来代替前面提过的名词
The weather here is warmer than that of Shanghai
The radios made in our factory are better than those in your factory
2)比较等级应注意避免和包括自己的对象比
比较级+than+
any other + 单数名词
all the other + 复数名词
anyone else
any of the other + 复数名词
3）如果形容词作定语修饰一个单数可数名词,一般将不定冠词a/an放在形容词之后
Our neighbour has _____ ours
A as a big house as
B as big a house as
C the same big house as
D house the same big as
4）比较级前一般不用冠词,但若表示“两者中较……时”比较级前要加定冠词若比较级后有名词,常在比较级前加不定冠词,表示泛指
Eg 他是两者中较高的一个
He is the taller of the two
她唱得真动听!我可从未听过比这更好的嗓音了
How beautifully she sings! I have never heard a better voice
4 三者或三者以上相比,表示最高级时,用“the +最高级”的结构表示,这种句式一般常有表示比较范围的介词短语
Zhang Hua is the tallest of the three
He works (the) hardest in his class
That was the least exciting football game I’ve ever watched
This hotel is the most comfortable I’ve ever stayed
注意：当最高级的前面无限定词the或有不定冠词a/an时,仅表示“很……,非常……”
Monday is my busiest day
星期一是我很忙的一天
Qingdao is a most (very) beautiful coastal city
青岛是一个非常美丽的海滨城市
比较级的一些其他用法
1 倍数表示方法
a) 倍数+as+形容词/副词原级+ as
b) 倍数+形容词/副词比较级+than
c) 倍数+ the + n + of
This rope is three times longer than that one
This rope is three times as long as that one
This rope is three times the length of that one
2 用形容词比较级的否定形式,从反面来表示最高级,通常译为“没有比……更……”
No other book has a greater effect on my life
没有哪一本书比这本书对我的影响更大的了
=This book has the greatest effect on my life
考例： —Go for a picnic this weekend, OK
--_____ I love getting close to nature
AI couldn’t agree more B I’m afraid not
CI believe not DI don’t think so
3 more and more 越来越… …
Our city is getting bigger and bigger
Our city is getting more and more beautiful
4 the more … the more … 越… …就越… …
The more you study, the more you know
The busier the old man is, the happier he feels
The more intelligent students are, the more quickly they understand ideas
5 可用下列词来修饰形容词的比较级
much a lot slightly a little almost far a bit still
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