问题描述：
一道英语选择题,英语高手请进.
All flights ___ because of the snowstorm,many passengers could do nothing but the train.
A.had been canceled B.have been canceled
C.having been canceled D.were canceled
请问这道题选哪个,为什么?请说明原因,
All flights ___ because of the snowstorm,many passengers could do nothing but the train.
A.had been canceled B.have been canceled
C.having been canceled D.were canceled
请问这道题选哪个,为什么?请说明原因,
问题解答：
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