Question

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.

Answer 1

第二句 I don't have a bag 对。
这是一般时，在这里 have 是一般动词=do，因此否定句用 don't
简例正句为：I do sth ,则否定句为：I don't do sth。
如果将原句改成完成时：I have had a bag.(I have done sth)
则否定形式为：I have not had a bag.(I have not done sth)
因此搞清楚 have 的功能就不容易发生错误。

Answer 2

后面的是对的,have not 后面应该跟动词,所以第一句明显错误

Answer 3

都对
若have后直接加not,代表你把它看做情态动词
如果加do否定，则是行为动词

Answer 4

I don't have a bag这个对，
have 的否定是加助动词不是加not

Answer 5

后者对，如果用前者应该是I have no bag。