问题
选择题
We don’t write to each other regularly，but we do keep in
touch by telephoning _____.
A．at a time
B．once
C．at once
D．once in a while
答案
答案：D
once in a while“间或，偶尔”;at a time 每次，一次；once 一旦；at once 立刻，马上。题意为：我们不经常相互写信但我们偶尔会通电话。