the house was started before she went to Africa and now it is still under construction.A.

问题补充：

the house was started before she went to Africa and now it is still under construction.

A. Working

B. Working at

C. Working on

D. Work on

答案：

A. Working

B. Working at

C. Working on

(答案→)D. Work on

解析：考查work做名词的用法：句意：房子的工作在她去非洲前就开始了，现在还在建设中。选D。