He was busy writing a story only once in a while to smoke a cigarette.A. to stopB. stopp

问题补充：

He was busy writing a story, only once in a while to smoke a cigarette.

A. to stop

B. stopping

C. to have stopped

D. having stopped

答案：

A. to stop

B. stopping

C. to have stopped

D. having stopped

解析：此题考查非谓语动词作状语的用法。句意：他在忙于写一个故事，只是偶尔停下来抽支烟。Only 在这里是连词 “只是”。

此题学生易误选A。only / just +不定式用来作状语通常表示出乎意料的结果，而此句很显然不是。