Don't keep the lights ___ all night long .If you don't use them .turn them off

问题描述:

Don't keep the lights ___ all night long .If you don't use them .turn them off
OK I see
A off B on Cdown D up

B.on
根据句意,这里指的是,别让灯一直亮着,所以用副词on
全句意为:别让灯通夜亮着.如果没用灯的话,就关掉.