Geometry

Question Analysis:
This question shifts from proof to properties of parallelograms.
The main focus is identifying always-true angle facts about parallelograms.

Key Concept Explanation：
Key parallelogram angle properties：
• Adjacent angles are supplementary
• Opposite angles are equal
• The sum of all interior angles is 360°

Step-by-Step Solution:
A: Opposite angles are congruent → always true ✅
B: Each adjacent angle pair sums to 180° → always true ✅
C: All 90° angles → only in rectangles and squares ❌
D: Opposite angles are equal, not supplementary → ❌
E: Interior angle sum = 360° in any quadrilateral → always true ✅

Commo...