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
网友回答
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。