One filled with excessive and mistaken enthusiasm in cause

A. Martyr

B. Pedant

C. Fanatic

D. Patriot

Answer: Option C

Solution(By Examveda Team)

One word substitute is Fanatic.

Martyr: a person who is killed because of their religious or other beliefs.
Pedant: a person who is excessively concerned with minor details and rules or with displaying academic learning.
Fanatic: a person filled with excessive and single-minded zeal, especially for an extreme religious or political cause.
Patriot: a person who vigorously supports their country and is prepared to defend it against enemies or detractors.