Which of the following sets of probabilities is possible for outcomes a, b, c, and d, given that they are disjoint?
a) P(a) = 0.2, P(b) = 0.3, P(c) = 0.4, P(d) = 0.3
b) P(a) = 0.1, P(b) = 0.4, P(c) = 0.3, P(d) = 0.2
c) P(a) = 0.3, P(b) = 0.3, P(c) = 0.3, P(d) = 0.3
d) P(a) = 0.5, P(b) = 0.5, P(c) = 0.2, P(d) = 0.3