Final answer:
The subject is Spanish, and the correct answer is 'a. vive'
Step-by-step explanation:
The subject of the question is Spanish.
The correct answer is a. vive.
In Spanish, the verb 'vivir' means 'to live'. The subject 'Mi vecina' is the third-person singular form, so the correct verb form is 'vive'.
Learn more about Spanish verb conjugation