Concept:The relationship in the analogy is antonym (direct opposite).
Explanation:Zenith is the highest point; Nadir is the lowest point. They are opposites.
Similarly, Success needs a word that is its exact opposite.
Failure (Option A) is the direct opposite of Success.
Objective (Option B) means a goal, not an opposite.
Gain (Option C) is a synonym of Success, not an antonym.
Career (Option D) is a related concept, not an opposite.
Therefore, only Failure preserves the antonym relationship.
Answer:Option A: Failure