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PHR-MODAL
（认为某事道义上正确，尤用于提出或征求建议或意见）应当，应该
You use ought to to mean that it is morally right to do a particular thing or that it is morally right for a particular situation to exist, especially when giving or asking for advice or opinions.
例句
Mark, you've got a good wife. You ought to take care of her...
马克，你娶了个好妻子，应该好好待她。
The people who already own a bit of money or land ought to have a voice in saying where it goes...
已经有点钱财或土地的人应当对其走向有发言权。
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PHR-MODAL
（认为某事可行或重要，尤用于提出或征求建议或意见）应当，应该
You use ought to when saying that you think it is a good idea and important for you or someone else to do a particular thing, especially when giving or asking for advice or opinions.
例句
You don't have to be alone with him and I don't think you ought to be...
你不必单独跟他呆在一起，而且我认为你也不该这样。
You ought to ask a lawyer's advice...
你应当征求一下律师的意见。
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PHR-MODAL
（认为某事确实，或预计某事发生或已经发生）应该/应该已经
You use ought to to indicate that you expect something to be true or to happen. You use ought to have to indicate that you expect something to have happened already.
例句
'This ought to be fun,' he told Alex, eyes gleaming.
“这应该会很有趣！”他对亚历克斯说，两眼闪闪发光。
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PHR-MODAL
（表示某事本应如此，但实际情况未必）应该
You use ought to to indicate that you think that something should be the case, but might not be.
例句
By rights the Social Democrats ought to be the favourites in the election. But nothing looks less certain...
社会民主党按理应该最有希望赢得这次选举，但一切从未如此不确定过。
Though this gives them a nice feeling, it really ought to worry them.
虽然这让他们感觉良好，但他们其实应该为此担心。
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PHR-MODAL
（表示从已知情况推测某事已经发生，但不确定）应该
You use ought to to indicate that you think that something has happened because of what you know about the situation, but you are not certain.
例句
He ought to have reached the house some time ago.
他应该早就到房子那儿了。
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PHR-MODAL
（与过去分词连用，表示预期的事未发生或预计的情况并非如此）本该，本当
You use ought to have with a past participle to indicate that something was expected to happen or be the case, but it did not happen or was not the case.
例句
Basically the system ought to have worked...
其实这套系统本应发挥作用的。
The money to build the power station ought to have been sufficient.
建设电站的资金本该足够了。
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PHR-MODAL
（与过去分词连用，表示未做本应该做的事情）本该，本当
You use ought to have with a past participle to indicate that although it was best or correct for someone to do something in the past, they did not actually do it.
例句
I realize I ought to have told you about it...
我意识到自己本该把这件事告诉你的。
Perhaps we ought to have trusted people more...
也许我们本当对人多一些信任的。
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PHR-MODAL
（礼貌地告知某人自己必须做某事）该，得
You use ought to when politely telling someone that you must do something, for example that you must leave.
例句
I really ought to be getting back now...
现在我真得回去了。
I think I ought to go.
我想我该走了。