18.4 Probability models. Which of the following is true of any legitimate probability model?
(a) The probabilities of the individual outcomes must be numbers between 0 and 1, and they must sum to no more than 1.
(b) The probabilities of the individual outcomes must be numbers between 0 and 1, and they must sum to at least 1.
(c) The probabilities of the individual outcomes must be numbers between 0 and 1, and they must sum to exactly 1.
(d) Probabilities can be computed using the Normal curve.