I want to ring him＿＿＿to know the reason why he rang＿＿＿while I was speaking yesterday. A.

问题补充：

I want to ring him＿＿＿to know the reason why he rang＿＿＿while I was speaking yesterday.

A. up； off

B. back； up

C. up； down

D. on； off

答案：

(答案→)A. up； off

B. back； up

C. up； down

D. on； off

解析：ring sb. up意为“给某人打电话”；ring off的意思是“挂断电话”。