The correct answer is D. Defamation.
Obloquy is a word that means “harsh criticism or abuse.” It is often used to describe negative statements that are made about someone’s character or reputation. Defamation is a legal term that refers to the act of making false statements about someone that damage their reputation.
Forgetfulness is the inability to remember something. Prejudice is a negative attitude towards a person or group of people based on their race, religion, or other characteristics. Conference is a meeting of people to discuss a particular topic.
While all of these words can be negative, only defamation is a synonym for obloquy.