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I don't think/believe that.. 其中的not是对宾语从句进行否定而不是对主句否定。(否定前移)。that可省略。

我认我/相信…不...I don't think it will rain.我认为天不会下雨。

I don' t think that... I don' t think he should give up learning English.我认为他不应该放弃学习英语。Give up放弃、辞去、投案自首

我认为/想/觉得...不...He has got a fever. I don' t think he will go for a picnic tomorrow. 他发烧了。我想他明天不会去野餐了.

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