Which of the following are probability distributions? Why? (a) RANDOM VARIABLE X PROBABILITY 2 0.1 -1 0.2 0 0.3 1 0.25 2 0.15 (b) RANDOM VARIABLE Y 1 1.5 2 2.5 3 PROBABILITY 1.1 0.2 0.3 0.25 -1.25 (c) RANDOM VARIABLE Z 1 2 3 4 5 PROBABILITY 0.1 0.2 0.3 0.4 0.0