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