首先,这个故事讲的是过去的事情,所以be肯定不能用现在时,而必须用过去时.其次,如果用与陈述语态相同的时态,表示其发生（或出现）的时间与陈述语态所发生的时间大致相同（从语法角度考虑,此处是可以用过去时was的）；如果用过去完成时态,表示其发生（或出现）的时间比陈述语态所发生的时间更早,也就是相当于汉语的“早就需要...”.
it have been necessary 和 it is necessary 的区别?请问下句中it had bee
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