The experts from the zoo were convinced that the animal was a puma,but where had 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
答
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.