问题
单项选择题
They happened to ______ for Tianjin when we got there.
A. leave
B. have left
C. leaving
D. had left
答案
参考答案：B
解析：[专家点评] happen to后接动词原形，所以先排除C、D，而不定式表示的动作发生于过去，故选B。
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They happened to ______ for Tianjin when we got there.
A. leave
B. have left
C. leaving
D. had left
参考答案：B
解析：[专家点评] happen to后接动词原形，所以先排除C、D，而不定式表示的动作发生于过去，故选B。