英语反意疑问句I think it's impossible for him to finish it in ten m

I think it's impossible for him to finish it in ten minutes, 【isn't it】?
解释：
1、这里考察的是反意疑问句.
2、当陈述部分含I think (believe, suppose...)that... 结构时,其反意疑问句须与从句的主、谓语保持一致,注意主句的主语必须是第一人称.例如：
I don't think he will come, will he?
我认为他不会来,对吗?
3、当陈述部分所含的否定词是通过加前缀或后缀构成的,其后的反意疑问句依然用否定结构.例如：
It is unfair, isn't it?
这不公平,是吧?
4、impossible 表示“不可能的”,是由possible前面加否定前缀“im-”构成的,后面的反意疑问句依然用否定,由此正确答案应该是：isn't it.