答：1．should 表示“劝告”，“建议”或“义务”时，译作“应当”， He should take care of his parents as they are old enough not to live on themselves. 由于父母亲老了，不能自理，他应当照顾他们。 ought to，接动词原形表示“有义务”或“必要”做某事，译为“应当，应该” 2．should have done在虚拟语气中表示“责备或后悔”” ought to have done sth, should have done sth 本应该做某事，而事实上并没有做。否定句表示"不该做某事而做了"。 You ought to (should) have been more careful in this experiment. He ought not to have thrown the old clothes away.（事实上已扔了。） 3．在这两个方面，用法基本相同，ought to 在语气上比should 要强。 4．Should还表示“预测”和“可能” He should be there now. 他可能到了。 5．Should在虚拟语气的用法中，用于从句中。 1） It is demanded / necessary / a pity + that…结构中的主语从句的谓语动词要用should 加动词原形， should 可省略。 句型： (1)suggested It is (2)important that…+ (should) do (3) a pity (1)suggested, ordered, proposed, required, demanded, requested, insisted； + (should) do (2)important, necessary, natural, strange a pity, a shame, no wonder (3)It is suggested that we (should) hold a meeting next week. It is necessary that he (should) come to our meeting tomorrow. 2）在宾语从句中的应用 在表示命令、建议、要求等一类动词后面的从句中。 order, suggest, propose, require, demand, request, insist, command, insist + (should) do I suggest that we (should) hold a meeting next week. He insisted that he (should ) be sent there.
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