To determine the most popular brands of tea consumed by Americans, a survey is conducted in a busy downtown location at lunchtime. Which of the following is NOT a potential bias in the sampling method?
a. Urban office employees are not representative of the general population. b. The results could be influenced by national brand teas available in the area. c. A lunchtime survey does not reflect peoples' tastes at other times of the day. d. The survey must include call-in and online responses.