These are noodles.This is soup.对吗.为什么?

this soup is n___ （These three) pieces of luggage is yours.用is对吗?还是用are.为什么?并且 为什么this is a XXX改复数,有时改成these are 有时又改成they are? these(this)后面接着is还是are? His favourite food is noodles 为什么用is 不用are My favourite food is noodles.为什么noodles是复数,而前面确用is不用are? this is my( ).these are my parents and this is 用That is...This is...thoes are...these are...造句! this is 与these are 的区别,该怎样讲解 this is 与these are this is 后加"a pen "还是"pen ",为什么"this is paper"可以不加?"these are This is a boy and a girl.为什么不说these are a boy and a girl. This are her brother?这个说法对吗?那These are her brother?