.He was about to leave the telephone rang; was from his mother.A. when; thatB. before; whi

问题补充：

.He was about to leave the telephone rang; was from his mother.

A. when; that

B. before; which

C. when; it

D. before; this

答案：

A. when; that

B. before; which

(答案→)C. when; it

D. before; this

解析：句意：他即将离开这是电话响了，是母亲打来的。句型： be about to do …when，即将做某事，正在那时，第二空用it ，指代前面的电话，所以选C。