(·安徽高考)It be the vocabulary that caused you the problem in the exercise because you k

问题补充：

(·安徽高考)It be the vocabulary that caused you the problem in the exercise because you know a lot of words.

A. may

B. couldn

C. should

D. needn

答案：

A. may

(答案→)B. couldn

C. should

D. needn

解析：选B考查情态动词的用法。句意：你难以完成那道练习题不可能是词汇量的原因，因为你掌握了大量的词汇。根据原因状语从句because you know a lot of words可知，主句应该是否定的，A项和C项可排除；needn 表示“不必”，不符合题意。此处表示可能性，故选B。