请在 下方输入 要搜索的题目:

Before the first non-stop flight made in 1949, it________necessary for all planes to land for refueling.


A、wouldbe;
B、hasbeen;
C、hadbeen;
D、wouldhavebeen

发布时间:2025-08-02 06:20:09
推荐参考答案 ( 由 题搜搜 官方老师解答 )
答案:has been
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