How to determine candidate keys from record schema and functional dependencies?

If I have a schema say R={A,B,C,D} and functional depen开发者_如何学Cdencies say {B->C, D->A} will my set of candidate keys be {B,D} or {BD}?

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If B were a candidate key, you'd have to be able to derive these functional dependencies from the ones given in the problem.

• {B->A}
• {B->C}
• {B->D}

Can you do that?