i am in China为什么要加am

i am in China为什么要加am i am not in this school.为什么要加in. I come from china.可以说I am from china.为什么这里不加be动词am了? 为什么i am wanna be with you要加am I am from the USA为什么要加am I am busy yesterday为什么加am 为什么I后面要加am? I am from china I am in 13 years old 要不要加s 为什么 i come from china i后面还加am吗 英语好的进,I am in company.I live in company.I am from China. Now I am in China,so I can speak_____little Chinese.