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题目内容
（三门峡职业技术学院英语读写）
Before the first non-stop flight made in 1949, it ________ necessary for all planes to land for refueling.
A.would be
B.has been
C.had been
D.would have been
A.would be
B.has been
C.had been
D.would have been
参考答案
