The sheep( )one after another since last week.

问题描述:

The sheep( )one after another since last week.
(has disappeared / have disappeared / are disappearing / are disappeared)
这题应该选什么,说出正确答案的理由和其他三个选项为什么不选的理由,

have disappeared
首先这句话的意思是羊儿们从上周起一个接一个的消失了
所以句首的sheep应该是负数,排除第一个答案
其次since last week是现在完成时的特征词,所以排除三四,因为他们是现在进行时和一般现在时