on and off

副词 on and off:

1. not regularly
   同义词：off and on

1. Since most of them have never had an opportunity to use computer, the training began with turning on and off the computer. Basic computer and Internet skills were the main courses offered, according to the trainer.
   据负责培训的老师介绍，由于这些女教师大多数从来没接触过电脑，所以培训班将从开关机器教起，主要进行计算机基本操作和网络知识的讲座以适应不同学员的水平。
2. It rained on and off all day.
   整天断断续续地下著雨。