I am going to be a reacher,为什么一定要用be,不能用do?

I am going to be a singer i am going to be I am going to be a singer的问句 I,am,to,going,teacher,be,a连词成句 I am going to be a worker.(改为同义句) going am to solider be I a连词成句 I am going to be a fashion designer Because__________________________________________________ I am going to be a photographer译成汉语 I am going to be taller是什么意思 i am going to be teller i am going to be crazy I am going to write a r and send it to newspapers(r开头的单词 I with my sister _ to the park.A.is going B.are going C.am going D.be going 今晚去看电影为什么是 I'am going to the cinema tonight而不是I'am going to see a film tonight?be going to 的具体用法? What are you going to be,Sarah?I am going to be a TV reporter.（改为第三人称） I am going to be a reacher,为什么一定要用be,不能用do? i'd like to help sick people.i hope ()a doctor.A.i am B.i am going to C.to be D.will be i am going to be sick为什么要用be?