Up till then they ________ at the airport for more than two hours, because their flight was delayed due to the bad weather．A.waitedB.have waitedC.had waitedD.have been waiting
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C解析看到时间状语up till now，这句句子的时态一定是用现在完成时；同样，看到时间状语up till then，这句句子的时态一定是用过去完成时。