核心问题
She is late. What ____ have happened to her?
A. should B. must C. can D. would
答案为 C(can)。但是 can have happened 是什么意思呢？
词典解答
can 在这里仍是表示“可能”。can have done 表示从现在的眼光看来“过去可能发生了某事”，而且其结果与现在有关。can have done 大都用在否定句和疑问句中：
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Where can he have gone? 他能去哪了呢?
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She's two hours late — what can have happened? 她已经晚了两个小时了, 可能发生了什么事呢?