语法总结
本课语法重点
表示猜测和推断的情态助动词must和can't（2） must与can't不仅能表达对现在和将来的猜测和推断，而且能表达对过去的猜测和推断——这时可用 must have been表示肯定的推断，用can't have been（而不是mustn't have been）来表示否定的推断，如后面跟进行时则表示对过去正在进行的动作的猜测。请看例句： You must have been driving at seventy miles an hour. 你当时肯定正以每小时70英里的速度行驶。 I didn't see it. I must have been dreaming. 我没看见。我当时一定是在胡思乱想吧。 She can't have been 29.She must have been 36. 她那时肯定不会是29岁，她一定36岁了。 He can't have been reading. He must have been sleeping. 他那时肯定不是在看书，他准是在睡觉。
例：表示猜测和推断的情态助动词must和can't（2） must与can't不仅能表达对现在和将来的猜测和推断，而且能表达对过去的猜测和推断——这时可用 must have been表示肯定的推断，用can't have been（而不是mustn't have been）来表示否定的推断，如后面跟进行时则表示对过去正在进行的动作的猜测