这个句子是强调句型,即it is /was +被强调部分+which /that /who +句子剩余部分。 从你所给的例句,可知,后面从句应该是用一般过去时, It was the first time that 后面就用过去完成,
过去完成时这不是强调句.只是一个固定句型It is the first time that +从句(用现在完成时)It was the first time that +从句(用过去完成时)
过去完成时