Classification — antonyms vs near-synonyms: Select the pair that is NOT an opposite pair: Day : Night, Up: Down, Across : Along, Small : Large.

Introduction / Context:
Three pairs are classic antonyms (opposites). One pair contains two words that are related but not opposites. The technique is to check whether substituting “not X” meaningfully yields Y. Genuine antonyms usually satisfy this quick negation test; near-synonyms or orthogonal terms do not.

Given Data / Assumptions:

• Day ↔ Night — temporal opposites.
• Up ↔ Down — directional opposites.
• Small ↔ Large — size opposites.
• Across vs Along — prepositions describing traversals with different orientations; not opposites.

Concept / Approach:
Antonyms negate each other on the same dimension. “Across” typically means from one side to the other (often perpendicular to a reference), whereas “along” means following the length or direction of something (parallel). They describe different directions of motion but are not contrary values of a single scale, and “not across” does not equal “along.”

Step-by-Step Solution:
1) Day vs Night → opposite states of a daily cycle.2) Up vs Down → opposite vertical directions.3) Small vs Large → opposite size magnitudes.4) Across vs Along → different spatial relations, not opposites.

Verification / Alternative check:
Try sentence substitution: “Walk across the road” vs “walk along the road.” The actions differ but one is not the negation of the other. This confirms C is the outlier.

Why Other Options Are Wrong:
They are standard, uncontroversial antonym pairs used in reasoning exams.

Common Pitfalls:
Treating any two related prepositions as opposites. Many prepositions are orthogonal (neither contrary nor complementary).

Final Answer:
Across : Along