A、It is a survival technique for babies. B、To ease hostilities. C、To make parents feel relaxed. D、To fight diseases. A

M: Well, you seemed to be having fun watching the movie?
W: Yeah, it was good fun. I think it kept me in stitches right from the start.
M: You know, whenever I watch comedy, I always like to know why it is that people like to laugh. I mean, why does it feel so good to laugh?
W: Yeah, I heard from my biology professor that even after centuries of scientific research, no one knows for sure why human beings and just a few other primates laugh.
M: I read somewhere that Charles Darwin thought that laughter, which begins with small babies, was like an evolutionary "reward" to the mother and father. Baby’s laughter sounded and felt so different from crying, he believed, that even prehistoric parents must have interpreted it as a sign of well-being, kind of like the purring of a kitten. The parents enjoyed the laughter, which encouraged them to continue caring for the child.
W: Yes, apparently researchers have also found that it has a positive effect on many patients and that it produces certain hormones that actually switch on the body’s immune system and actually help fight off diseases. So it could be to help fight off disease.
M: I also heard that some psychology professor from the University of Maryland, studied the laughter that takes place in conversations between men and women and found that most laughter takes place when males are talking and females are listening. Men are more likely to make jokes than women are, and women are more likely to laugh at them than men are.
W: If only your jokes were funny, I might laugh more and lit that pattern.
M: Well, I’ve heard that apes also like laughing.
W: I heard that too. Chimpanzees, apes, orangutans and a few other primates laugh, but no other animals do. I’ve seen them laugh at zoos, when tickling each other, and when playing chasing games. Their laugh sounds like rapid panting, but I’ve been assured it’s a kind of laughing.
M: Which reminds me I’d better go back before my roommates eat all the chicken I left out in the kitchen!