Final answer:
The verb form that correctly completes the sentence is 'estudió'
Step-by-step explanation:
The correct verb form to complete the sentence is estudió.
This is because the subject of the sentence is Juan, a singular third-person noun. When the subject is singular third-person, the verb form needs to match, which in this case is estudió.
An example sentence using this verb form is: Juan estudió periodismo en la universidad hace dos años.
Learn more about verb forms in Spanish