Which sentence would serve as the topic sentence for a paragraph about student jobs?

kelly bags groceries at the corner market.

the students in my class work a variety of after-school jobs.

the schwartz brothers mow lawns for their neighbors.

I believe the correct answer would be option two. 
"The students in my class work a variety of after-school jobs"
This is the best answer to begin your essay or paper. 

"Kelly bags groceries at the corner market." &
"The Schwartz brothers mow lawns for their neighbors."
Is a supporting topic, which could be used in another paragraph to support your main sentence. 

Good luck I hope this helps