knocking at the door before entering ,please 这句话哪里了

单句改错 who is the men knocking at the door Someone is knocking at the door.____ is it? I tried knocking at the front door but nobody ___it Listen!_______(有人）is knocking at the door. Someone is knocking at the door,but who can____ be? Please do not e_____without knocking at the door. Please do not ------without knocking at the door怎么填 someone is knocking at the door.It might be the posyman.为什么用is knocking There is someone knocking at the door.为什么用“knocking”,要加“ing”? i seem to hear someone knocking at the door,knocking为什么要加ing 为什么是is knocking：Who is knocking(knock) at the door?it's me. Don't come in before knocking at the door.before 后面的 knocking用的对吗? Someone is knocking at the door.同义句改写：There is ___ ___ at the door. who was knocking at the door just now?还是who knocked at the door just now? Listen!I hear someone knocking at the door.Listen!_____ ______ a knock on the door. 27 If nobody answers the door bell ,try ___ the back door.A to knock at b.to knock c.knocking at d.knocking 需要详细分析 Someone is knocking at the door._must be TomSomeone is knocking at the door._must be Tom A.that B.It C.He D.This Did you heard someone knocking at the door?为什么要用at?RT3Q