should, ought to可通用,但在疑问句中常用should。 1. you should / ought to go to class right away. 2. should i open the window? 3) 表示推测 should , ought to (客观推测), must(主观推测)。 1.he must be home by now. (断定他已到家) 2.he ought to/should be home by now.(不太肯定) 3. this is where the oil must be.(直爽) 4. this is where the oil ought to/should be.(含蓄) 八、 情态动词+不定式完成式(have done) 1) can / could + have done