I come from china.可以说I am from china.为什么这里不加be动词am了?

I come from china.可以说I am from china.为什么这里不加be动词am了? i come from china i后面还加am吗 I am from china I am Leo come from China.I am Leo from China.哪个正确? I come from China和 I am from China意思一样吗 I come from China.的同义句是?试卷上我写了I am from China.不对 you,he and I [are/is/come/am] from china I am come from China. 没有语法错误吗? I am from (China).括号部分提问, i am from china改一般疑问句 I am from china 改为一般疑问句 I am from China 改为否定句