听力原文： Why do we cry？ Can you imagine life without tears？
Not only do tears keep your eyes lubricated, they also contain a substance that kills certain bacteria so they can't infect your eyes. Give up your tears and you lose this on-the-spot defence.
Nor would you want to give up the flood of extra tears you produce when you get something physical or chemical in your eyes. Tears are very good at washing this irritating stuff out.
Another thing you couldn't do without your tears is cry - from joy, anger, or sadness.
Humans are the only animals that produce tears in response to emotions. And most people say a good cry makes them feel better.
Many scientists, therefore, believe that crying somehow helps us cope with emotional situations. Tear researcher William Frey is trying to figure out how it happens.
One possibility, he says, is that tears discharge certain chemicals from your body, chemicals that build up during stress. "When people talk about 'crying it out,' I think that might actually be what they are doing," he says.
If Frey is right, what do you think will happen to people who restrain their tears？ Boys, for example, cry only about a quarter as often as girls once they reach their teenage years. And we all cry a lot less now than we did as babies.
Could it possibly be that we face less stress？ Maybe we've found other ways to deal with it. Or maybe we just feel embarrassed.
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A. Why people hold back their tears.
B. Why people cry.
C. How to restrain one's tears.
D. How tears are produced.