by the time the earthquake ended,millions of people had become homeless.为什么加had?直接became可以吗?

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by the time the earthquake ended,millions of people had become homeless.为什么加had?直接became可以吗?
by the time the earthquake ended,millions of people had become homeless.
为什么加had?
直接became可以吗?

by the time the earthquake ended,millions of people had become homeless.为什么加had?直接became可以吗?
直接became不可以.
因为by the time 是过去完成时的标志,看见这个标志,就一定要用过去完成时.
过去完成时的标志有:
1、by + 时间点
By last year,we had learnt 2 000 English words.
2、by the time + 句子,就是上面这一句
语法书里过去完成时部分重新翻一遍,语法书一定要经常翻,不翻就忘了

因为前面有个by,在地震停的那一刻,无家可归是停的那一刻之前就发生的事.就是过去完成时,该动作发生在"停止"这个动作之前.
有by the time这个条件就不可以直接became

过去完成时

不可以这里有两个动作,无家可归是在地震结束“之前”的状态,所以这里要用前面那个动作之前的时态,而前面结束这个动作是一般过去时,所以无家可归要用过去完成时。