Though there are few Chinese___have heard of the Great Wall,many of them haven't been there yet

A:as B:who C:that D:but

你好。应该是 D
FEW / NO / LITTLE - -- -+ BUT- - -- 双重否定结构的定语从句
=== Though there are MANY Chinese WHO have heard of the Great Wall,
又如：in our library, there are NO books BUT he has read.===in our library, there are no books that he has not read.

C

that/who这是定语从句，从句的关系代词可以用that（人、物通用）也可以是who（专指人）

选C 这里先行词Chinese前被不定代词few等修饰时，引导词只能用that,不能用who 。这是定语从句的一个原则。