I don't believe he is a bad student.I believe he isn't a bad student.这两个句子都对吗?

I don't believe he is a bad student.I believe he isn't a bad student.这两个句子都对吗?
I don't believe he is a bad student.I believe he isn't a bad student.这两个句子都对吗?

I don't believe he is a bad student.I believe he isn't a bad student.这两个句子都对吗?
I don't believe he is a bad student 是对的.think,believe 等宾语从句,要否定转移.

语法没有问题
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这2句中国人看意思一样，第一句正确，第二句错误，英语中遇到believe,think,guess,suppose必须否定前移