听力原文：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, but it's much more common than carbon.
M: Oh, I see.
What is the woman studying？

A. The basic structure of atoms.
B. The basic structure of molecules.
C. The basic structure of neutron.