关于椎体骺板缺血坏死的描述哪项不正确（）

A.椎体骨骺出现迟缓，呈分节状，密度增高，轮廓不清，形态不规则

B.椎体前部楔形改变，驼状脊柱后突

C.椎体前部上下缘呈阶梯状改变

D.椎间隙变窄

E.脊柱后突畸形永久存在

You can think of many cases         Chinese students obviously know a lot of English words and expressions but can’t express themselves freely.

A．when.

B．which.

C．as.

D．where