It is strange that the small boy work out such a difficult exercise which is even hard t

问题补充：

It is strange that the small boy work out such a difficult exercise, which is even hard to settle for adults.

A. should

B. might

C. could

D. would

答案：

A. should

B. might

C. could

(答案→)D. would

解析：情态动词辨析。A. 应该 B.可能 C.能够；can的过去时态 D.将要。句意：很奇怪，这个小男孩想要算出如此难的一道，甚至成年人都很难解决的练习。选D。