问题
选择题
Before the first nonstop 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
答案
答案：C
题目分析：考查时态：句意：在1949年世界上首次不间断飞行之前, 所有飞机有必要的降落加油。说明“有必要”是在1949年之前，用过去完成时，选C。
点评：时态的考查主要看上下文的语境和句子的关键词。这题的关键是时间状语Before the first nonstop flight made in 1949。