A、  B、  C、  B要对换座提议进行正确回应。(A)不适合用来回应提议，主语they也表述得不是很明确。(B)在对提议表示赞成的同时又提出了自己的意见，所以是正确的答案。而(C)则是答非所问。

Is the supply room on the left side?
(A)Yes, next to the copier.
(B)There should be some left.
(C)No, we’re out of space.

Let’s change seats.
(A)I hope they can exchange them.
(B)Great. I’d rather sit closer to the front.
(C)They’ve already been renovated.