Final answer:
The correct form of the verb vivir is vive in the sentence provided.
Step-by-step explanation:
In the sentence "Tu hermano __ en San Francisco," the correct form of the verb vivir to be used is vive. This is the third person singular form of the verb vivir, which agrees with the subject 'Tu hermano' (Your brother). The correct sentence would then be 'Tu hermano vive en San Francisco.'
Learn more about Verb forms in Spanish