2.39 Grade distributions: Each row in the table below is a proposed grade distribution for a class. Identify each as a valid or invalid probability distribution by using properties of probability distributions. A B C D F (a) 0.3 0.3 0.3 0.2 0.1 (b) 0 0 1 0 0 (c) 0.3 0.3 0.3 0 0 (d) 0.3 0.5 0.2 0.1 -0.1 (e) 0.2 0.4 0.2 0.1 0.1 (f) 0 -0.1 1.1 0 0 a) Distribution (a) is a/an: Valid probability distribution Invalid probability distribution b) Distribution (b) is a/an: Valid probability distribution Invalid probability distribution c) Distribution (c) is a/an: Valid probability distribution Invalid probability distribution d) Distribution (d) is a/an: Invalid probability distribution Valid probability distribution e) Distribution (e) is a/an: Invalid probability distribution Valid probability distribution f) Distribution (f) is a/an: Valid probability distribution Invalid probability distribution