问题补充：
The old man, abroad for twenty years, is on the way back to his motherland.
A. to work
B. working
C. to have worked
D. having worked
答案：
A. to work
B. working
C. to have worked
(答案→)D. having worked
解析：此题考查非谓语动词形式如何体现时间顺序。不定式表将来、打算；动词ing形式表主动、进行；由于已经工作，所以选D项。
