【问】 I____asleep while I was working because it took me a long time to realize that the tele-phone was ringing.

A. should fall B. ought to fall

C. had to fall D. must have fallen(Nelson，250B)

正确答案为D。但我不明白fall asleep中的fall是什么词，具有什么含义。

【答】 fall除作“跌”、“降落”解(如：The young child fell into the lake.)之外，还可作“变为”、“成为”解。fall用作这个意义时，是个连系动词，可与形容词和名词连用：

1. At the President's entry everyone fell silent. (GPU)

总统一入场，大家都安静了下来。

2. The post of headmaster fell vacant. (GPU)

校长的职位空缺了。

3. She fell an easy prey to him.(ALD)

她轻易地成了他的牺牲品。

4. One after another，all three of them fell asleep. (Bennet)

他们三个人一个接一个地都睡着了。

请做下面的英语试题：

No sooner had he gone to bed than he fell ____.

A. sleeping B. sleep

C. slept D. asleep(全国高考英语试题，80)