In a certain geographical market, Sprint wishes to increase its market share by taking a survey of customers of its competitor, Pacific Bell, in an effort to find out which parts of its service are least satisfactory. Which of the following procedures would be most appropriate for obtaining a statistically unbiased sample?

A. Survey a random selection of people chosen from a list of Sprint's customers.

B. Survey a random selection of people chosen from a list of Pacific Bell's customers.

C. Place a newspaper advertisement asking for survey participants, and then randomly choose 100 people from those who respond.

D. Call local phone numbers and ask people who answer if they are satisfied with their phone service.