Classify the following attributes as discrete (D) or continuous (C), qualitative (QL) or quantitative (QN), and as binary (B) or nominal (N) or ordinal (O) or interval (I) or ratio (R). Circle your selection in each of the three sets that classify the attribute. (a) {D, C}, {QL, QN}, {B, N, O, I, R}: Number of students enrolled in a course. (b) {D, C}, {QL, QN}, {B, N, 0, 1, R}: Names of the students enrolled in a college. (c) {D, C}, {QL, QN}, {B, N, O, I, R}: Level of happiness {very happy..... very unhappy). (d) {D, C}, {QL, QN}, {B, N, 0, 1, R}: Shoe size (in whole sizes)