Let R = (A, B, C, D, E, F) be a relation scheme with the following dependencies C -> F, E -> A, EC -> D, A -> B. Which of the following is a key of R?
- A. CD
- B. EC
- C. AE
- D. AC
Answer: B. EC
Explanation: Closure of EC: E->A, so {E,C,A}. A->B, so {E,C,A,B}. C->F, so {E,C,A,B,F}. EC->D, so {E,C,A,B,F,D}. EC covers all attributes.