My father is a farmer but yours . . . . . an advocate.

Answer: Option B

When you are speaking of or for yourself, use "am." When you are talking about a person or a thing (in the singular), use "is." When you are talking to a person, and when you are talking about other people or things (in the plural), use "are." Here, it is singular as one is compared to the other. Hence, is will be used.