he has been working so hard he could answer such a difficult question. A. No wander B.

问题补充：

he has been working so hard . he could answer such a difficult question.

A. No wander

B. No wonder

C. why

D. because

答案：

A. No wander

(答案→)B. No wonder

C. why

D. because

解析：本题的含义是他一直学习很努力，怪不得他能够回答出这么难的问题，no wonder表示难怪或怪不得的意思，符合本题的含义，故本题选B。