作业帮求英语达人告诉我答案以及为什么选这个答案.要详细一点.Before the first non-stop flight was 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
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求英语达人告诉我答案以及为什么选这个答案.要详细一点.Before the first non-stop flight was 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
求英语达人告诉我答案以及为什么选这个答案.要详细一点.
Before the first non-stop flight was 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
求英语达人告诉我答案以及为什么选这个答案.要详细一点.Before the first non-stop flight was 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
C.had been
解析：在过去的某个时间段（ the first non-stop flight was made in 1949）之前,发生的事情（all planes to land for refueling.）,即本题考察的是 过去的过去 应该用什么时态
A.将来式 .显然不符合
B.现在完成时.现在完成时强调的是过去的事情延续到现在,对现在产生影响,此题明显看 出于现在没有什么关系,不选.
C.过去完成时.强调发生的动作对过的某个时间（1949）产生的影响,符合.
D.一般用于虚拟语气.与此题不符（虚拟语气一般是假设,题中句子只是一般的陈述,没有假设成分）,故不选.
C had been
前面有了before，之前，而在过去式之前发生的事情就要加have/had（过去完成时）
而would代表没有发生但会发生的事情
但是后半句描述的事情已经发生了，就不能用would
C,根据题意选择过去完成时