【问】 I forgot to ask him about it.与I forgot asking him about it.有什么区别?

【答】 在动词forget之后跟不定式时，动词不定式结构所表示的动作或事件本应发生在for-get (忘记)这个动词所表达的心理过程之后，也就是说，动词不定式结构所表示的动作或事件仅仅是一种潜在的可能性。forget的词义使这种潜在可能性未能变为现实，换句话说，动词不定式结构所表达的动作并未发生。I forgot to ask him about it.意为：我忘了去问他这件事。而在动词forget之后跟动名词时，动名词结构所表示的动作或事件是发生在forget(忘记)这个动词所表达的心理过程之前，也就是说它已成为既成事实(先前事件)。I forgot ask-ing him about it.意为：我问过他这件事，但我却忘记了。

类例：

1.{He has forgotten to visit the Great Wall. 他忘了去游长城(实际上没有去)。He will never forget visiting the Great Wall. 他将永远不会忘记游长城这件事(实际已游览过)。

2.{I forgot to close the door. 我忘记关门了。I forgot closing the door. 我关上了门，但我忘记了。

3. I shall never forget hearing her singing that song.

我永远不会忘记听她唱那支歌时的情景。

4.{I forgot to meet her in 1980. (=“I did not meet her because I forget that I had arranged to do so. ”) 1980年我忘了去会见她(我没有去会见她，因为我忘了曾作过这种安排)。I forgot meeting her in 1980. (=“I met her，but the meeting subsequently escaped my memory. ”)(CGEL) 我忘记了曾在1980年见过她(我曾见过他，但是随后忘记了这件事)。

5. There’s one thing I’ve forgotten to tell you.

有件事我忘记告诉你了。

6. She nearly forgot to give him a tip for his service.

她几乎忘了给他的服务付小费。

请做下面的英语试题：

—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(全国高考英语试题，1991)