An assignment of probabilities must obey which of the following?
(a) The probability of any event must be a number between 0 and 1, inclusive.
(b) The sum of the probabilities of all outcome in the sample space must be exactly 1.
(c) The probability of an event is the sum of the outcomes in the sample space that makes up the event.
(d) All of the above.
(e) Only (a) and (b) are true.