“Rectangle” and “Pentagon” differ by the number of sides (4 vs 5). Choose the option that mirrors this polygon-sides progression.

Introduction / Context:
Geometric analogies often highlight changes in the number of sides of polygons. A rectangle (4 sides) to pentagon (5 sides) increases side count by 1. We must find a pair that similarly moves from a polygon with fewer sides to one with one more side.

Given Data / Assumptions:

• Rectangle → 4 sides; Pentagon → 5 sides.
• Triangle → 3 sides; Rectangle → 4 sides.

Concept / Approach:
“Triangle : Rectangle” preserves the +1 side progression (3 → 4). Other options are mismatches of concepts (line segments vs perimeter), properties vs figures, or incomparable figure types (circle has 0 straight sides).

Step-by-Step Solution:
1) Abstract the relation as “polygon with n sides → polygon with n+1 sides.”2) Map triangle (3) to rectangle (4).3) Select “Triangle : Rectangle.”

Verification / Alternative check:
Counting sides confirms the intended increment.

Why Other Options Are Wrong:

• Diagonal : Perimeter: Properties/measures, not polygons.
• Side : Angle: Elements, not specific figures.
• Circle : Square: Not a +1 side relation; circle has no straight sides.

Common Pitfalls:
Choosing related geometric terms that do not maintain the “sides count” logic.

Final Answer:
Triangle : Rectangle