为什么说I have a bag 却不能说I am have a bag同志们,谢啦

为什么说I have a bag 却不能说I am have a bag同志们,谢啦 I have a bag with books in it.(“in it” 不能省略)?书上说in it 不能省略?为什么?in it 是修饰book的吗?with books in it 应该是修饰bag的定语吧?不太懂! I have a bag. i have a bag with books in it为什么in it 不能省略,i have a bag with books 这样不对吗 为什么不能说i have a best friend,his name is Tom I have a bag.一般疑问句能变成：Have I a bag? I have a bag.改为否定:I have not a bag.I don't have a bag.哪个对?Have的否定变化. i have no feet 改成 i am HAVE NOT feet 顺便说下为什么不能， I have no time为什么不能说i have not time? I HAVE A CHOICE TO CHOOSE..与..为什么不能说I HAVE A CHOICE TO BE CHOSE 什么时候可以用STH TO BE DONE呢? look i have a new bag.my bag is newest than your bag.( ) abaut mary's bag.her bag ( ) the ( )of all. I have a computer game in my bag (一般疑问句) M什么 I have a look at your new bag? I don't have a bag.改为肯定句是什么 I,a,cap,have,in ,bag ,my.连词成句 have a good time 为什么加a?nice weather前面却不能加a? I have a headache能不能说成I have a sore headI have a headache能不能说成I have a sore head回答能或不能 Miss Li ______ a bag.I ______a sketch book.A.have,has B.is ,have C.has,have为什么选c?