The correct answer is option (B):
advocate
The correct answer is advocate because a proponent is someone who supports or argues in favor of something. An advocate also supports or pleads for a cause or proposal. They both share the same fundamental meaning of promoting or backing an idea or action.
The other options are incorrect:
* Predecessor means someone who came before you in a position or role.
* Conspirator is someone involved in a secret plan to do something harmful or illegal.
* Informer is a person who gives information to the police or other authority about something.