5. [15 points] Consider a relation schema R (A, B, C, D). For each of the following sets of functional dependencies, please identify the best normal form that R satisfies (INF, 2NF, 3NF, or BCNF), and point out the normal form violations. (a) {A B, BC DA C} (b) {AB C, AB DC A,D B} (c) {ABC D, D A)