我查了一下郎文,关于sure和certain 还是有一些细微的差别的。 sure: if you are sure about sth, you feel that it is almost certainly true or correct e.g. you have worked so hard, I'm sure you'll do well in your exams. are you quite sure that he understand your instructions?
certain: completely sure that sth is true e.g. are you absolutely certain you didn't leave your key at home?
第二个题,从句子的结构上来看是明显的冗余 第三个题,... is ...(什么/怎么样是什么/怎么样) 在这种情况下是OG要求的平行结构,具体的你可以找一下og,有很多的例句。