It is fifty-four years since the People's *______

问题描述:

It is fifty-four years since the People's *______
A.founded B.was founded C.has founded D.has been founded
答案应该是A,为什么?请说明原因,

found 建立,因为新中国建立的事实已经完成,所以过去式加ed 就可以了,排除C,D.
新中国成立是主动的,不能说新中国被成立,所以排除B