一般来说,must be/do对于现在的推测,反意疑问句对be/do进行提问,而must have done句后的反意疑问句要看主句是否有具体的时间状语,如 He must have finished his work, hasn't he? He must have finished his work yesterday, didn't he? 第一句中没有具体时间状语,...
情态动词所表达的可能性程度:must/can't should/shouldn't might/may (not) 另外两个"类情态词的形式:"need/needn't; have to/don't have to 最自然的虚拟状态:由should/would+原型时态(不含时间只含状态) 本质上是过去将来时:即,...