【题目】--- It was a relief when the kids were found.
--- Yeah. Their parents _____ have been very worried while they were lost.
A. need B. should
C. must D. might
在线课程【答案】C
【解析】考查情态动词。A. need需要； B. should应该；C. must 必须； D. might或许。上句：孩子被找到这是一个极大的安慰。下句：是的，在他们丢失期间父母一定非常担忧。must have done表示对过去事情有把握的肯定推测，“一定是做某事了”，故选C。