1)dave,a student in ....., is.....
2)dave,students in.....,is....
3)dave,student in...,is

Which one is correct?
I think the first one is correct because since "student" is a countable noun, an indefinite or definite noun must be placed before it. However, from my practice exercise, the model answers are both 1 and 3. Could anyone help me with this?

Thanks a lot!