Today we’ll discuss a number of cases beginners of English fail to use the language prop

问题补充：

Today, we’ll discuss a number of cases beginners of English fail to use the language properly.

A. which

B. as

C. why

D. where

答案：

A. which

B. as

C. why

(答案→)D. where

解析：where在此引导定语从句，修饰先行词cases，where的意思相当于in which。类例：There are cases where the word “mighty” is used as an adverb. 在一些情况下，mighty一词可用作副词。