HELP PLS Which answer choice best corrects the run-on sentence?

I need to study for the geography exam I need to improve my grades.


I need to study for the geography exam, I need to improve my grades.

I need to study for the geography exam because I need to improve my grades.

I need to study. For the geography exam I need to improve my grades.

I need to study for the geography exam I need. To improve my grades.