One who knows two languages:

A. Bigot

B. Bigamy

C. Bilingual

D. Brittle

Answer: Option C

Solution(By Examveda Team)

The one word substitution is Bilingual.

Bigot : a person who is a blind supporter of his religion.
Bigamy : the offence of marrying someone while already married to another person.
Brittle : hard but liable to break easily.
Bilingual : speaking two languages fluently.