Question

【题目】These diagrams are especially helpful when we have a concrete problem ______ at hand.

A. be solved B. to solve C. solved D. being solved

Answer 1

【答案】B

【解析】B 考察非谓语动词。句义：如果我们手边没有解决的具体问题，你们这些数据就非常有用，have在此表示有，后面接不定式的形式。