问题补充：
Many air flights because of the eruption of the volcano, in case, many passengers had no choice but to take a train.
A. had been cancelled; which
B. have been cancelled; what
C. had been canceling; that
D. have been canceling; where
答案：
(答案→)A. had been cancelled; which
B. have been cancelled; what
C. had been canceling; that
D. have been canceling; where
解析：考查时态及定语从句。句意：由于火山的爆发，许多航班都被取消了，在这种情况先，许多乘客只有坐火车了。根据语境可知主句描述的是过去某个时间前已经完成的动作，故用过去完成时态。在非限定性定语从句中，指代前文整句话内容时，只能用which做引导词，故选A。
