Beforethe first non-stop flight made in 1949, it（） necessary for all planes to land for refueling.
Beforethe 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
正确答案：C
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时间：2023-11-12 11:12:27