单选题Before the first non-stop flight made in l949, it ______ necessary for all planes to land for refueling.Awould be Bhas beenChad been Dwould have been
单选题
Before the first non-stop flight made in l949, it ______ necessary for all planes to land for refueling.
A
would be
B
has been
C
had been
D
would have been
参考解析
解析：
本句的时间状语为过去的某个时间点以前，所以要用过去完成时态。
本句的时间状语为过去的某个时间点以前，所以要用过去完成时态。
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