问题补充:
—The light in the office is still on.
—Oh, I forgot
A. turning it off
B. turn it off
C. to turn it off
D. having turned it off
答案:
A. turning it off
B. turn it off
(答案→)C. to turn it off
D. having turned it off
解析:分析forget doing sth. 意为“忘了曾经做过某事”,forget to do sth. 意为“忘记去做某事”。