Analogy — choose the pair that continues the “polygon with n sides to polygon with n+1 sides” pattern as in Rectangle : Pentagon.

Introduction / Context:
“Rectangle : Pentagon” moves from a four-sided polygon to a five-sided polygon (n to n+1). The question asks for another pair that mirrors this numeric progression within the polygon family.

Given Data / Assumptions:

• Rectangle has 4 sides; pentagon has 5 sides.
• We need a pair that moves from a polygon with n sides to the next with n+1.
• Only polygon-to-polygon comparisons are relevant.

Concept / Approach:
Check which option represents a move from 3 to 4, or in general from a lower-sided polygon to the next one. “Triangle : Rectangle” shifts from 3 sides to 4 sides, matching the pattern and the direction (simpler to more complex polygon).

Step-by-Step Solution:

Verification / Alternative check:
Try other options: if they are not both polygons or do not involve n to n+1, they fail the mirrored structure. “Triangle : Rectangle” is the only clean match.

Why Other Options Are Wrong:

• Side : Angle — not polygons; unrelated attributes.
• Diagonal : Perimeter — polygon properties, not distinct polygons.
• Circle : Square — circle is not a polygon; relation is categorical mismatch.

Common Pitfalls:
Confusing polygon attributes with polygon types, or picking pairs that do not reflect a consistent incremental step within the same category.

Final Answer:
Triangle : Rectangle