Geometry

Question Analysis:
This question tests your ability to identify invalid or insufficient conditions for classifying a parallelogram.
The main focus is recognizing which conditions do not guarantee a parallelogram.

Key Concept Explanation:
While many properties can belong to parallelograms, not all of them are useful for proving one.

Step-by-Step Solution:
A: True — one of the valid conditions
B: True — diagonals bisect each other ⇒ sufficient
C: True — this is the classic condition you’ve been studying
D: Diagonals congruent ⇒ isosceles trapezoid

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