at the end of the meeting,it was announced that an agreement ___.a,has been reached b,had been

题目

at the end of the meeting,it was announced that an agreement ___.a,has been reached b,had been
reached c,has reached d,had reached选b为什么不选a?这句话的意思是什么?

答案

因为前边用“it was”,表明是过去发生的事,需要用过去完成时,选b.
整句话的意识是：在会议的尾声,一个协议被宣告已经达成.