副詞 on and off:

1. not regularly
   同義詞：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.
   據(jù)負責(zé)培訓(xùn)的老師介紹，由于這些女教師大多數(shù)從來沒接觸過電腦，所以培訓(xùn)班將從開關(guān)機器教起，主要進行計算機基本操作和網(wǎng)絡(luò)知識的講座以適應(yīng)不同學(xué)員的水平。
2. It rained on and off all day.
   整天斷斷續(xù)續(xù)地下著雨。