Take another look at the passage:
To save enough money to pay tuition, Tanisha keeps a strict budget. She never carries more than three dollars in her wallet. To avoid making impulse purchases like a pizza or CD that will cause her to come up short when registration begins.
You chose the first part, To save enough money to pay tuition, Tanisha keeps a strict budget. This part has a main clause: Tanisha is the subject; keeps is the verb. A fragment will not have a main clause.