He was about to leave the office for home someone knocked the door and asked for some hel

问题补充：

He was about to leave the office for home someone knocked the door and asked for some help.

A. until

B. while

C. as

D. when

答案：

A. until

B. while

C. as

(答案→)D. when

解析：

试题分析:句意：他正要离开办公室回家这时有人敲门求助。固定句型：be about to do …..when 正要做某事……这时，选D。