Geometry

Question Analysis:
This tests corollary properties of parallelograms derived from the "opposite sides parallel" condition.

Key Concept Explanation:
Opposite sides parallel ⇒ Parallelogram ⇒ Opposite angles ≅ (a core theorem).
Other properties (e.g., diagonals ⊥) depend on stricter conditions (e.g., rhombus).

Step-by-Step Solution:
Option A: False (only rectangles have 90° angles).
Option B: False (true for rhombuses/squares only).
Option C: Correct (all parallelograms have ≅ opposite angles...