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Consider a relation scheme R = (A, B, C, D, E, H) on which the following functional dependencies hold: {A $\rightarrow$ B, BC $\rightarrow$ D, E $\rightarrow$ C, D $\rightarrow$ A}. What are the candidate keys R?

1. AE, BE
2. AE, BE, DE
3. AEH, BEH, BCH
4. AEH, BEH, DEH

(d) AEH, BEH, DEH

using the given functional dependencies and looking at the dependent attributes, E and H are not dependent on any. So, they must be part of any candidate key. So, only option is D. If we see the FD's, adding A, B or D to EH do form candidate keys.
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