Suppose the administration at your school has hired you to help with a survey to find out how students feel about opening a new recreation center on campus. They provide you with a random sample of 100 students and a phone number for each one. Some of them are land-lines, and some are cell phones. You call the 100 numbers and interview the person who answers the phone. Explain which one of the “difficulties and disasters” in sampling you are most likely to encounter and how it could bias your results.