In geometry, a postulate (or axiom) is a statement that is assumed to be true without proof.
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Statement #1: A line contains at least two points. This is a foundational concept in geometry and is accepted as true, making it a postulate.
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Statement #2: All right angles are equal. This is also a fundamental property in geometry, accepted as true. However, it can be derived from other concepts (such as the definition of right angles), and is often referred to in the context of theorems rather than a postulate.
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Statement #3: a + b = b + a reflects the commutative property of addition in arithmetic, but it is not a geometric postulate.
Based on this analysis, the postulate is:
Statement #1 is a postulate.