I was on the point of going to bed Mr. Zhang rang.A. asB. whenC. whileD. and

问题补充：

I was on the point of going to bed Mr. Zhang rang.

A. as

B. when

C. while

D. and

答案：

A. as

(答案→)B. when

C. while

D. and

解析：因为句中的并列连词when = just at that time, 意为“这时(突然)”。