Step 1: Understanding the word "smother".
"Smother" means to suffocate or to cover something completely, often in a way that prevents it from getting air or being able to grow or function properly. It conveys the idea of stifling or suffocating something.
Step 2: Analyzing the options.
(A) Abstain: "Abstain" means to refrain from doing something, which is not related to "smother". It does not fit as a synonym.
(B) Frighten: "Frighten" means to make someone afraid, which is unrelated to "smother". It is not a synonym.
(C) Unleash: "Unleash" means to release or let something go, which is the opposite of "smother". This is not a synonym.
(D) Stifle: "Stifle" means to suppress or prevent something from growing or developing, which is a synonym of "smother". It fits the context perfectly.
(E) Spread: "Spread" means to extend or disperse something over an area, which is the opposite of "smother". This is not a synonym.
Step 3: Conclusion.
The correct synonym for "smother" is (D) Stifle, as both words convey the idea of suppressing or preventing growth.