A、They are describing a new dustbin. B、They are discussing the protection of environment. C、They are collecting used batteries.

M: Have you noticed the new dustbin downstairs, at the entrance of the main building?
W: Yeah, of course. It looks funny, though, like a battery. What’s it for? Is it really for garbage?
M: Not really. Actually it’s a dustbin for used batteries.
W: Used batteries? What do you mean by that? Why do we need a special dustbin for used batteries?
M: Well, you know there are still a lot of heavy metals left in used batteries? So by recycling the batteries, we can not only make full use of the metals left, but also prevent the environment from being polluted.
W: Oh, I see. Can this work? Our efforts are too insignificant.
M: Even though we are not ecologists or biologists, there is still a lot we can do. The Student Union is sponsoring a one-month program called "Green Movement", which is aimed at making more and more students aware of serious environmental problems we are facing now.
W: Sounds quite exciting—"Green Movement". What, for example, can I do?
M: Well, quite a lot. For one thing, you can stop using those plastic meal-boxes and disposable wooden chopsticks. Plastic meal-boxes do great harm to the environment and disposable chopsticks are a big waste of forest resources. Well, there will be a lecture tomorrow afternoon at four o’clock. You may attend if you are interested.
W: Tomorrow afternoon...let me think...yeah, I happen to be free. I will go there.