they must have finished the work by the end of last month,___?a,mustn't they b,haven't they c,hadn't they d,didn't they

问题描述:

they must have finished the work by the end of last month,___?
a,mustn't they b,haven't they c,hadn't they d,didn't they

对过去已经做了的事情的推测,选C

选d
must have done sth.后面若有过去时间,如本题的“last night”,则反意疑问句用一般过去时形式:“didn't + 主语”

选C,当情态动词must表推测时,其反义疑问句要根据实际情况来判断,本题的时间状语是by the end of last month,应与过去完成时连用,还原一下本题应为:They had finished the work by the end of last month.所以要选C.