选C.这是对过去的猜测.在表示猜测的否定时,情态动词要用can或could,不能用must；should若用在should not have done中表示“本不该做（但已经做了）”；would not have done用于虚拟语句中,比如：Without your help,I would not have succeeded.没有你的帮助,我不会成功的.注：would have done表虚拟时,不可置于从句中,而应在主句中使用.