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If `A → B` and `B → C` both hold in a relation, then Armstrong's axioms let you conclude
AC → A (the relation flips)
BB → A (any FD is symmetric)
CAC → B (augmentation collapses into transitivity)
DA → C (transitivity chains the two arrows)
Answer & Solution
Correct answer: D. A → C (transitivity chains the two arrows)
Transitivity is exactly this rule: `A → B` and `B → C` together imply `A → C`. The other options invert or mis-apply: FDs are NOT symmetric, augmentation adds the same attribute to both sides (not collapsing), and reversing the arrow is not a valid step in general.
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