下列各组物质中，前者属于单质，后者属于化合物（　　）

A．食盐   食醋

B．青铜器   空气

C．氧气   二氧化碳

D．水    铜丝

重新排列句子使其成为一段完整的对话。

A. What's your favourite food?

B. Amy, it's time for lunch now.

C. I like tofu, too. But fish is my favourite.

D. Yes. It's 12 o'clock. Let's go to the canteen.

E. I like tofu very much. It's healthy for me.

F. OK. Some tofu and fish, please.

正确的顺序是: B __________________________________