答案：C

题目分析：从时间状语over the past twenty-four hours可以得知用完成时，但找的动作还很有可能继续下去，故使用现在完成进行时。句意：为了找到那个失踪的男孩，那对夫妇在过去24个小时里尽一切所能在找。

点评：时态是高考常考内容。时态题的考查要注意关键词，同时要注意具体语境。

即学即练：－Why didn’t you give me a call last night?

－Well, I couldn’t. My phone _____________.

A. was being repaired                    B. had been repaired

C. would be repaired                     D. was repaired

选A