单选题
17.
All flights ______ because of the storm, they decided to take the train.
A、
having canceled
B、
having been canceled
C、
were canceled
D、
have been canceled
【正确答案】
B
【答案解析】
本句中的逻辑主语与分词间是被动关系，且独立结构中行为已经发生，应用过去分词的完成时。
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