6.Kent is supposed to be a gifted footballer () there has ev

6.Kent is supposed to be a gifted footballer () there has ever been.
A that B what C it D who
18.Let's discuss only such questions () concernded everyone of us.
A what B that C as D and
答案给的是AC,第一题我不知道为什么,第二题as一般只能用于非限定定于从句,在用于限定性定语从句时候应该只有固定的such as,the same as等才能用.麻烦给出一定解析.