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PHR-MODAL
（認為某事道義上正確，尤用于提出或征求建議或意見）應當，應該
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...
馬克，你娶了個好妻子，應該好好待她。
The people who already own a bit of money or land ought to have a voice in saying where it goes...
已經有點錢財或土地的人應當對其走向有發言權。
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PHR-MODAL
（認為某事可行或重要，尤用于提出或征求建議或意見）應當，應該
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...
你不必單獨跟他呆在一起，而且我認為你也不該這樣。
You ought to ask a lawyer's advice...
你應當征求一下律師的意見。
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PHR-MODAL
（認為某事確實，或預計某事發生或已經發生）應該/應該已經
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.
“這應該會很有趣！”他對亞歷克斯說，兩眼閃閃發光。
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PHR-MODAL
（表示某事本應如此，但實際情況未必）應該
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...
社會民主黨按理應該最有希望贏得這次選舉，但一切從未如此不確定過。
Though this gives them a nice feeling, it really ought to worry them.
雖然這讓他們感覺良好，但他們其實應該為此擔心。
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PHR-MODAL
（表示從已知情況推測某事已經發生，但不確定）應該
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.
他應該早就到房子那兒了。
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PHR-MODAL
（與過去分詞連用，表示預期的事未發生或預計的情況并非如此）本該，本當
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...
其實這套系統本應發揮作用的。
The money to build the power station ought to have been sufficient.
建設電站的資金本該足夠了。
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PHR-MODAL
（與過去分詞連用，表示未做本應該做的事情）本該，本當
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...
我意識到自己本該把這件事告訴你的。
Perhaps we ought to have trusted people more...
也許我們本當對人多一些信任的。
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PHR-MODAL
（禮貌地告知某人自己必須做某事）該，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...
現在我真得回去了。
I think I ought to go.
我想我該走了。