I can think of many cases students obviously knew a lot of English words and expressions

问题补充：

I can think of many cases students obviously knew a lot of English words and expressions but couldn’t write a good essay.

A. why

B. which

C. as

D. where

答案：

A. why

B. which

C. as

(答案→)D. where

解析：可联系答案网客服索取。