the first time I saw it was three years ago.要过去时还是完成时?why?

问题描述:

the first time I saw it was three years ago.要过去时还是完成时?why?

这道题的正确答案是:
当然要用过去时,
因为三年前,是一个时间点,且发生在过去,所以要用过去时