As a 9th grader (going into 10th grade), is it smarter to take a creative writing cl or an advertising clas?

CW would be my choice, you would have take that anyway for advertising or a novelist. There is also a chance that the school would let you take all 3, drop study hall might a option. I would check around and see if a summer cl is available or a night course offered by a local college or vocational school.