I was just falling asleep there was a loud knock at the door.A. whileB. whenC. untilD. as

问题补充：

I was just falling asleep there was a loud knock at the door.

A. while

B. when

C. until

D. as soon as

答案：

A. while

(答案→)B. when

C. until

D. as soon as

解析：while当……时，强调主从动作同时发生；when当……时；until直到；as soon as一……就。句意：当传来大声的敲门声时，我刚睡着。结合语境可知我睡着在先，故选B。