17.3 Randomness. Random phenomena have which of the following characteristics?
(a) They must be natural events. Man-made events cannot be random.
(b) They exhibit a clear pattern in very many repetitions, although any one trial of the phenomenon is unpredictable.
(c) They exhibit a clear pattern in a single trial but become increasingly unpredictable as the number of trials increases.
(d) They are completely unpredictable; that is, they display no clear pattern no matter how often the phenomenon is repeated.