Relational Schema

Q21.

Let R = (A, B, C, D, E, F) be a relation scheme with the following dependencies C \rightarrow F, E \rightarrow A, EC \rightarrow D, A \rightarrow B. Which one of the following is a key for R?
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Q22.

From the following instance of relation schema R(A,B,C), we can conclude that :
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Q23.

Consider a schema R(A,B,C,D) and functional dependencies A\rightarrowB and C\rightarrowD. Then the decomposition of R into R1(AB) and R2(CD) is :
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