18. W: Martin, are you doing anything special for your presentation in political science tomorrow?

　　M: Not really, because the class so often turns into a discussion. I’ve decided to play it by ear.

　　Q: What does Martin plan to do?

　　Now you’ll hear two long conversations

　　Conversation One

　　M: How did you like yesterday’s astronomy class?

　　W: It was interesting, but the point she was trying to make seemed a little far-fetched.

　　M: Oh, that new theory that ocean water came from comets?

　　W: Yeah. Do you remember what it’s based on?

　　M: Some recent satellite photos, I think. Apparently, space satellites recently detected thousands of small comets colliding with earth’s outer atmosphere, almost 40,000 per day.

　　W: Ok, so they collide with the atmosphere. Then that’s what created the water?

　　M: It’s not that the collision created water. Comets contain water. They are made up mostly of cosmic dust and water. When they collide with the atmosphere, they break up and the water they contain rains down to earth. Ocean water came from that rain.

　　W: Oh, well, this morning, I asked my geology professor about that. He said that most geologists don’t accept it.

　　M: Why not?

　　W: Well, their research indicates that most of the water molecules from the comets will have burnt up as they fell through the atmosphere. Enough rain couldn’t have reached the earth to fill up the ocean.

　　M: Well, do the geologists have an alternative theory to explain where ocean water came from?

　　W: Yeah, he said the more traditional view is that ocean water came from volcanoes.

　　M: From volcanoes?

　　W: Right! As the volcanic fumes are mostly steam. And they claim that it was volcanic steam that created the oceans, not rain from comets.

　　Questions 19 to 21 are based on the conversation you have just heard.

　　19. What did recent photographs from a space satellite indicate?

　　20. According to the new theory, where did ocean water come from?

　　21. What group disagrees with the new theory described in the conversation?

　　Conversation Two

　　M: Hi, Sarah. What’s up?

　　W: Oh, hi, I just got out of a history class. I had to give a presentation.

　　M: How did it go?

　　W: Terribly. I’m sure I made a fool of myself.

　　M: Why? Weren’t you prepared?

　　W: No, it was not that. It’s just I get so embarrassed and nervous whenever I have to speak in front of a group of people. I stand up and my face gets red and then I get even more nervous because I know everyone can see me blushing.

　　M: It’s not so bad to blush.

　　W: But it happens all the time. If the professor asks a question and I know the answer, I blush like crazy if he calls on me. Doesn’t that ever happen to you?

　　M: No, not really. Maybe you should just try to forget about the people. Look at something else in the room like the exit sign.

　　W: I guess I could try that but I doubt it’ll help.

　　M: You know, we talked about it in psychology class. Blushing, even though it’s involuntary, is more or less a learned behavior.

　　W: What do you mean?

　　M: Oh, children hardly ever blush at all. And among adults, supposedly, women blush more than men.

　　W: I wonder why?

　　M: I don’t know, but I had a friend at high school, Brian Smith. It was really easy to make him blush. He turned red whenever a waitress would ask him for his order.

　　W: I’m not that bad. Well, I’ve got to get going for my next class. I’ll talk to you later.

　　Questions 22 to 25 are based on the conversation you have just heard.

　　22. What was the woman’s problem?

　　23. Why might looking at the exit sign help the woman?

　　24. What does the man say about children?

　　25. Why does the man mention his friend Brian?