A、They just stay in the room and turn on the air conditioner. B、They eat cool food. C、They roll into a kind of special mud. D、Th

M: Congratulations on completing your PhD in Zoology this week, Yael.
W: Well, we want to make sure listeners know they’re getting only the best information.
M: You must be proud.
W: I’m happy as a pig in mud.
M: Hey, there’s a good moment of science.
W: Why arc pigs happy?
M: No, why do pigs roll in mud? I mean, you’d never catch me doing that!
W: But I have seen you sweating.
M: Well, I guess so ...
W: Ever seen a pig do that?
M: Have I seen a pig sweat? Well ... I guess not. But what’s your point?
W: Pigs are doing the same thing when they roll in mud that we’re doing when we sweat.(14)They’re staying cool.
M: Staying cool?
W: Sure.(15)Humans get rid of excess heat by sweating. When the sweat evaporates it carries heat energy away from your body, which is why a sudden breeze feels cold when you are wet. Pigs don’t have sweat glands. They have to add moisture to their skins in order to get it to evaporate and take away heat.
M: And mud has moisture in it.
W: It sure does; otherwise it would be dry dirt. If there were water to splash in, the pig might choose that to cool off.
M: And that’s something even people do!
W: At every swimming pool in town.
Questions 13 to 15 are based on the conversation you have just heard.
13. What does the dialogue mainly about?
14. Why do pigs roll in mud?
15. According to the dialogue, how do human get rid of excess heat?