Meeting my uncle after all these year was an unforgettable moment I will always remember.

问题补充：

Meeting my uncle after all these year was an unforgettable moment ,I will always remember.

A. that

B. one

C. it

D. what

答案：

A. that

(答案→)B. one

C. it

D. what

解析：句意：这么多年后遇到我叔叔是我会永远难忘的时刻。这里需要代词指代an unforgettable moment，做它的同位语，one可以泛指前面的可数名词单数，that是特指可数名词单数和不可数名词，it是指同类同物，what不能引导非限制性定语从句，所以选B。