Recording 50
录音50
You will hear a lecture about hair.
你将听到一段关于毛发的讲课。
First, you have some time to look at questions 31 to 40.
首先，你有时间看看第三十一题至第四十题。
Now listen carefully and answer questions 31 to 40.
现在仔细听录音，并回答第三十一题至第四十题。
Good morning, and welcome to this lecture on hair which is a part of the human biology course.
早上好，欢迎大家来上这节关于毛发的课，这是人体生物学课程的一部分。
This lecture covers a number of facts about hair: its structure and what can affect the general health of hair.
这节课将涵盖关于头发的好几点知识：毛发的结构，以及影响毛发整体健康的因素。
So, first of all, what is hair and why do we have it?
首先，什么是毛发，为什么要有毛发？
If we look back at our ancestors, we'll see that they had a lot more hair on their bodies than we do now.
如果我们追溯到我们的祖先那一代人，我们就会发现，他们的毛发比我们现在可多得多。
And there are (or were) two main reasons for having hair. One is to provide warmth... but as humans have worn clothes for many years, body hair has significantly reduced.
长毛发主要有两个原因，第一是供暖……但由于人类已有多年穿衣史，体毛就大大减少了。
The other is for protection. And again this isn't as significant as it was once, but hair does still benefit areas of the body such as the head and around the eyes.
另一个原因是提供防护。重申一次，其防护作用以远不如前，但毛发对身体某些部位而言还是很有益处的，比如头部和眼周。
Now hair, whatever it is for and wherever it is on the human body, is composed mainly of a protein called keratin.
毛发，不论其用途和分布何处，其成分主要是一种叫角蛋白的蛋白质。
This, by the way, is also found in fingernails. In fact, it's keratin which makes them flexible and without it they would be very rigid.
顺便一提，角蛋白也存在于指甲中。实际上，正是角蛋白使毛发和指甲变得具有弹性，否则就会非常坚硬。
Another interesting fact about hair is that it is very strong, as strong as iron in fact.
关于毛发的知识中，还有一点比较有趣的是，毛发非常强韧，实际上相当于铁的强度。
One single strand can support a weight of up to 100 grams.
单单一根毛发能承受至多100克的重量。
This may not sound all that much, but a full head of hair can support up to 12 tonnes, which is the equivalent of a couple of elephants, which is simply amazing, though I advise you not to put this to the test!
这听起来可能不太多，但一整头头发最高可承受12吨，相当于两只大象的重量，这可太令人惊讶了。当然，我不建议你们去尝试。