Determine which of the following given values can serve as the values of a probability

distribution of a random variable with the range x = 1, 2, 3 and 4

a) f(1) = 0.25 , f(2) = 0.75 , f(3) = 0.25 , f(4) = -0.25

b) f(1) = 0.15 , f(2) = 0.27 , f(3) = 0.29 , f(4) = 0.29

c) f(1) = 1/19 , f(2) = 10/19 , f(3) = 2/19 , f(4) = 5/19

d) None of these