Function f: A → B is onto (surjective) if:
- Every b ∈ B is image of some a ∈ A
- Random
- Empty
- Always
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Correct answer: A. Every b ∈ B is image of some a ∈ A
**Surjection (onto):** range = codomain.
Every element of B has at least one preimage.
Bijection = injective + surjective.