单项选择题

[听力原文]6-7
W: What did you think of the lecture
M: I thought it was very interesting.
W: Did you really
M: Yes, didn’t you
W: Certainly not. I thought he talked a lot of rubbish.
M: So you think you know more than he does.
W: Well, take coal for instance.
W: What about it
M: Coal won’t become important again.
W: Why not
M: It’s too dirty. They won’t be able to find people to work down in coal mines in the future.
W: They’ll invent new kinds of machinery.
M: Nonsense. The only sort of power they’ll use in the future is atomic power.

What are the two people talking about（）

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