I was about to go to bed one of my old classmates made a call to me. A. whenB. asC. while

问题补充：

I was about to go to bed one of my old classmates made a call to me.

A. when

B. as

C. while

D. that

答案：

(答案→)A. when

B. as

C. while

D. that

解析：考查固定句式；固定句式be about to do sth when…正要做某事在这时…；句子的when是一个并列连词，表示“在那时…”；句意：我正要睡觉，在这时我的一个老同学来看我。故A正确。