Gexercise 19.7 suppose you are given a rebltion r \vith four attributes ab()d. f'or each of the following sets of fds, assurning those are the only dependencies that hold for r, do the following: (a) identify the candidate key(s) for r. (b) identify the best honnal forbl thatr satisfies (lnf, 2nf, : jnf, or benf). (c) if ii is not in bcnl~\ decolnpose it into a set of bcnf relations that preserve the dependencies. 1. c: - d, + a. 13 c 2. fj '-~-f c'. d --> a : 3. abc -~f d, d --> a 4. a -+ b. b(} ,. d. a ~. c 5. a13 c, ab···_··.• d. c -+ a, d·_·-+ 13