Final answer:
The correct answer is 'reprobar'.
Step-by-step explanation:
The correct answer to complete the sentence is reprobar. This word means 'to fail' in Spanish. Therefore, the complete sentence would be 'Tengo que estudiar mucho o voy a reprobar mi clase', which translates to 'I have to study a lot or I'm going to fail my class'.
Learn more about Completing a sentence in Spanish