once in a while

例句：

1. 1.She once in a while goes to the park for exercise.
   她偶尔去公园锻炼。
2. 2.He once in a while comes to our house for dinner.
   他偶尔来我们家吃晚饭。
3. 3.We should once in a while take a break from work.
   我们应该偶尔从工作中休息一下。