electricity usage can be limited by turning off computers be
electricity usage can be limited by turning off computers before going to sleep and remembering to turn off the lights before leaving a room 这句话里面的ing形式,如果让我自己来写的话我不会写,请问这是什么语法,什么时候可以像话中的那样.比如我自己写,我可能是before go to the sleep不会写成going