It was not until early this morning my father came back from work which surprised us. A.

问题补充：

It was not until early this morning my father came back from work, which surprised us.

A. when

B. where

C. that

D. who

答案：

A. when

B. where

(答案→)C. that

D. who

解析：考查强调句型。本题强调的是时间状语not until early this morning；句意：直到今天早晨早些时候，我的父亲才下班回来，这让我很惊讶。It is/was…that/who…是强调句型的基本结构，故C正确。