319. A company is marketing an investment opportunity to four potential customers. The company believes that its probability of making a sale is 0.7 for each of the first three customers but that it is only 0.2 for the fourth customer. The customers' purchases are independent of one another. Calculate the probability that at most two customers purchase the investment. (A) 0.18 (B) 0.39 (C) 0.57 (D) 0.71 (E) 0.82