They all looked so happy. They（）have succeeded after so many fai

They all looked so happy. They（）have succeeded after so many failures.
A、must
B、would
C、should
D、could
【正确答案】：A
【题目解析】：【应试指导】本题考查情态动词辩析?句意：他们定成功了。 must have done意为“一定做过某事”，表示对过去事情的肯定推测。根据句意，本题本题选A。