At ___he takes apples for lunch ,but one at___.A times;the time B times;a time C the time; the time

题目

At ___he takes apples for lunch ,but one at___.A times;the time B times;a time C the time; the time
D one time; a time 我想知道为什么选B,

答案

B
at times 有时
at a time 一次
有时他拿苹果当午饭,但是,一次只吃一个.