Geometry

Question Analysis:
This question tests recognition of rectangles from parallelograms.
The main focus is on diagonal length.

Key Concept Explanation:
A rectangle has diagonals that are equal in length.

Step-by-Step Solution:
A: Defines a rhombus
B: True for all parallelograms
C: Diagonal congruence confirms a rectangle
D: Perpendicular diagonals → rhombus

Option Analysis:
Only C directl...