he is a student , isn't it ?这是一个简单句,不过我不明白后面的 isn't it 又是一个句

我想问一个英语语法方面的问题,he is a student ,isn't he 这是一个简单句,不过我不明白后面的 Your clasemate is a boy ,isn't it?该句中“it”应用it还是he? LIFE IS GOOD这句的反问怎么问?是ISN'T IT It is a fine day today,isn't it?后面一句怎么读? 英语：it is a nice day,isn't it?这个isn‘t it 翻译的是：不是吗 还是： He isn't a student,is he?否定回答是Yes,he is .还是 No,he isn't. that is your twin brother,----?反义疑问句是 isn't he 还是isn't it? Isn't it a lovely day?的答语为什么是Yes,isn't it? john isn't a diligent student,for it is the third time he ha is that a goat no 一个空选测 isn;t A是in B 是 that C是it Is that boy Ted?A.NO ,he isn`t B.NO ,it isn`t.填那个 小菜一碟it is a piece of cake的同义句是什么 The new car isn't mine的同义句是