Question

I can't find the pen I was given. Have you seen ________?

1. A.
   it
2. B.
   one
3. C.
   this
4. D.
   that

Answer 1

A
it指代上文提到的单数名词，one指同类中的任一个，根据题意应指“我的那支笔”。所以one不适当。