—Where's that report?—I brought it to you you were in Mr.Black's office yesterday.A. ifB.

问题补充：

—Wheres that report?

—I brought it to you you were in Mr.Blacks office yesterday.

A. if

B. when

C. because

D. before

答案：

A. if

(答案→)B. when

C. because

D. before

解析：该空表示“当……的时候”，因此应填when引导时间状语从句。