that 在句子中做什么成分

问题描述:

that 在句子中做什么成分
It happened once ,however ,some 70 years ago ,that the gold cup was stolen a few days before the race.

你把插入语(however,some 70 years ago)去掉,变成It happened once that……
这句话是主语从句,It是形式主语,that作从句连词