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 cannot infect your eyes. Give up your tears, and you will lose this on-the-spot defense. Nobody wants 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 could not 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 believe that crying somehow helps us cope with emotional situations. One of the Tear researchers, Winked, 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. If Fred is right, what do you think will happen to people who restrain their tears? Boys, for in stance, cry only about a quarter as often as girls once they reach teenage years, and we all cry a lot less than we did as babies. Could it be possibly that we face less stress? Maybe we found another way to deal with it, or maybe we just feel embarrassed. What is the focus of the passage?