Step 1: Understanding the Question:
This question tests the candidate's understanding of prepositions that follow verbs denoting marital relationships in the passive voice.
The sentence describes the state of marriage of a subject to another person.
Step 2: Key Concepts and Grammar Rules:
In active voice, the verb ``marry'' does not take a preposition (e.g., ``He married an advocate'').
However, when using the passive voice or expressing a state of being married (using the auxiliary verb ``to be''), the adjective ``married'' is followed by the preposition ``to''.
Step 3: Detailed Explanation:
• Common Error: A very common error is to use ``married with'' due to direct translation from native or regional languages.
However, in standard English, ``married with'' is incorrect when indicating the person to whom someone is wed.
``Married with'' is only used in contexts like ``married with children'' (meaning married and having children).
• Option (C) - to: This is the correct fixed preposition to indicate the spouse of a person in a passive structure.
Thus, ``He is married to an advocate'' is correct.
• Options (A), (B), and (D): These do not convey the correct meaning and violate standard grammatical rules in this context.
Step 4: Final Answer:
The correct choice is Option (C) because ``to'' is the grammatically correct preposition.