Explicit undertaking to do something

A. Agreement

B. Decision

C. Settlement

D. Promise

Answer: Option D

Solution(By Examveda Team)

One word substitute is Promise.

Agreement: harmony or accordance in opinion or feeling.
Decision: a conclusion or resolution reached after consideration.
Settlement: an official agreement intended to resolve a dispute or conflict.
Promise: a declaration or assurance that one will do something or that a particular thing will happen.