情态动词后接进行式, 完成式和完成进行式: a) 情态动词可以和动词的进行式构成谓语, 表示”应该正在…”, “想必正在…”这类意思: Why should we be sitting here doing nothing? This isn’t what I ought to be doing. She might still be thinking about the question you raised. They must (may) be waiting for us, let’s hurry up. They can’t be using the room now. b) 情态动词有时和动词的完成形式构成谓语, 表示”应当已经…”, “想必已经…”这类意思: I should have thought of that. They shouldn’t have left so soon. She must have arrived by now. You needn’t have told them that. Where can (could) he have gone? He can’t have finished the work so soon. He may not have achieved all his aims. But his effort is praise- worthy. We ought to have give you more help. c) 情态动词间或也可以和一个动词的完成进行式构成谓语,表示”应当一直在…”, “想必一直在…”这类意思: They are sweating all over. They must have been working in the fields. They may have been discussing the problem this morning. You should have been waiting for us. Why haven’t you? She couldn’t have been swimming all day.
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