Liu Xiang’s breaking the world record was an exciting moment all of us will never forget.

问题补充：

Liu Xiang’s breaking the world record was an exciting moment, all of us will never forget.

A. that

B. one

C. it

D. what

答案：

A. that

(答案→)B. one

C. it

D. what

解析：考查定语从句。代词one是moment的同位语，all of us will never forget是省略了关系代词that 的定语从句；非限制性定语从句不用that引导，所以A项不对。