The experts from the zoo were convinced that the animal was a puma,but where had it come from 为什么不用where did it come from

问题描述:

The experts from the zoo were convinced that the animal was a puma,but where had it come from
为什么不用where did it come from

所用时态是过去完成时态,表示过去的过去,是在专家相信前,所以用这种时态;一般过去时表达不出这种意思。

had come是过去完成时,表示过去的过去发生的动作.原句中were convinced动作发生在come之后.