Question

—      you        who took my pen by mistake?

—Not yet.

1. A.
   Did; find
2. B.
   Did; find out
3. C.
   Have; found out
4. D.
   Have; found

Answer 1

C
由Not yet的答语可知应用现在完成时,find out是“查明”，此句的含义是你能查明是谁错拿了我的钢笔吗。