为什么leaving the TV or radio 后要加on?

为什么leaving the TV or radio 后要加on? leave before 7 o’clock,or you will miss the train.为什么用leave?不用leaving? The bus is leaving soon为什么要用is leaving? the teacher is waiting for the students leaving.为什么用leaving而不用to leaving from books,movies,the radio,the tv or the internet.为什么表示电器前都加the?on the internet也是 Do you like to watch TV or to listen to the radio?为什么不能改成watching TV or listening to theradio 为什么on TV 不是 on the TV watch tv 还是watch the tv 为什么 turn on the tv or open the magzine and you……turn on the tv or open the magzine and you_____advertisements showing happy familiesa.will often seeB.often see答案是b可是为什么不可以是a呢 I forgot the air tickets .---You are always leaving something .为什么用leaving 为什么不用leave, Did you get the news----the radio or ----- TV? The leaf is leaving .Is it that the wind's seek or the tree's unteta She is leaving the second week in july这句话为什么 leaving后面没有跟介词 Either you or your father( )TV in the evening. get help from nowspapers ,magazines,TV or the lnternet 急用! Other people listen to the r___ or watch TV. _______students watch TV three or four times a week.A MostB The mostC The someD The all为什么选A不选B? before leaving the room,he turned off the radio.这里为什么要用动名词leaving,而不是其原形?