Geometry

Question Analysis：
This is a concept-check question about which properties apply to all parallelograms.
The main focus is on distinguishing general from special parallelogram properties.

Key Concept Explanation：
In all parallelograms:
Opposite sides and angles are equal
Diagonals bisect each other
But diagonals are only congruent in rectangles and squares, not all parallelograms.

Step-by-Step Solution：
Eliminate true properties:
A, B, and C are always true
D is only true in rectangles, so it’s not always true

Option Analysis：
A. Opposite angles are equal ✅ Always true
B. Diagonals b...