达到气候顶极以前的一个相当稳定的演替阶段（）。
A.后顶极
B.前顶极
C.亚顶极
D.分顶极
参考答案：C
There was a lot of fun at yesterday’s party. You _______, but why didn’t you?
A．should come
B．may come
C．ought to have come
D．may have come
主要缺点
