单项选择题
M: What are you looking for
W: We’re studying the basic structure of molecules.
M: Just any molecules There are quite a few of them!
W: Yes, far too many. We’re only working with certain molecules that contain carbon and hydrogen.
M: What do you expect to learn from that
W: We’re trying to see the kinds of carbon molecules in which we can use silicon as a substitute.
M: What difference would that make
W: Silicon has a lot of the same properties as carbon, hut it’s much more common than carbon.
M: Oh, I see.
A．The kinds of molecules in which carbon may be replaced by silicon.
B．The importance of silicon.
C．The difference between molecules and silicon.