There is someone knocking at the door.为什么用“knocking”,要加“ing”?

There is always someone是什么意思 there are someone还是there is someonert is there someone here与 is someone here 一样么 Is there someone downstair?为什么用someone不用anyone? is downstairs there someone.连词成句 there is someone walking behind you? Is there anyone special?There is someone special.和There is a special one.哪个更好. someone复数单数someone is there.这里是is.someone like water.like是原形.糊涂糊涂. (It is)(There is) someone at the door.(It is)(There is) 选填,急 there is someone in the room 改否定句 there is someone in the classroom.改为否定句 急用! Look!There is someone _____(敲）at the door. There is someone downstairs的否定句是什么 there is someone knocing at the door改为否定句 the thief thinks there is someone at home and runs? there is someone live翻译中文s in my heart there is Someone in my heart 什么意思? listen!there is someone ()(sing)in that buildingsing的形式