.I’m sorry I stepped outside for a smoke. I was very tired.There is no for this

问题补充：

.--- I’m sorry I stepped outside for a smoke. I was very tired..

--- There is no for this while you are on duty.

A. reason

B. excuse

C. cause

D. explanation

答案：

A. reason

(答案→)B. excuse

C. cause

D. explanation

解析：名词辨析。A原因；B借口；C原因；D解释；句意：—对不起我要出去抽支烟。我太累了。—当你在值班的时候，不应该有这样的借口。根据句意说明B正确。