Let X = the number of nonzero digits in a randomly selected 4-digit PIN that has no restriction on the digits. What are the possible values of X? 0, 1, 2, 3, 4 0, 1, 2, 3, 4, ... 1, 2, 3, 4, ... 1, 2, 3, 4 0, 1, 2, 3