Which of the following functions makes the most sense as a model for the probability density representing the time (in minutes, starting from t = 0) that the next customer walks into a store?
(a) p(t) = {cos t 0 ≤ t ≤ 2π e^t−2π t ≥ 2π
(b) p(t) = 3e^−3t for t ≥ 0
(c) p(t) = e^−3t for t ≥ 0
(d) p(t) = 1∕4 for 0 ≤ t ≤ 4