look,the boy is chansing the dog 问一下 为什么必须用running after 而不用 catching请说明原因 谢谢

Look!the ( ) (30) boy is running fast. Look,the boy is falling _____the bike. Look at the boy.H___name is Tony. Look,the boy is piaying basketball______the gym. Look ,the boy is waiting in line.改同义句Look ,the boy is ------ ------ line. Look at the (P ).the boy in it is look at the boy. Look!The boy is ______the cake into two halves. Look!The boy is c____ his room.怎么填? 小学英语试题:Look!The boy __.Look!The boy __.A.is hungryingB.hungryedC.is hungry选哪个? Look,the boy is cutting in line的同义句Look,the boy is ____ ____ line The boy is so young that he can't look after himslfThe boy is not___ ____ to look after himself look at the boy reading a book 和look at the boy is reading book 那个对? The boy is too young to look after himself.(同意句）The boy is___ ___ ___to look after himself. look!the boy in blue---(look)smart look,the little boy ____in the lake.A.is swiming B.swims C.is swimming What is the boy doing?He is (look)at the public signs. Look,the boy is laughing (loud),but the girl is sitting (quiet).适当形式填空xx