A person who speaks or supports an idea

A. Pioneer

B. Adviser

C. Advocate

D. Ideologist

Answer: Option C

Solution(By Examveda Team)

One word substitute is Advocate.

Pioneer: a person who is among the first to explore or settle a new country or area.
Adviser: a person who gives advice in a particular field.
Advocate: a person who publicly supports or recommends a particular cause or policy.
Ideologist: someone who develops or supports a particular ideology.