A political action committee sends out a questionnaire to randomly-selected mailing addresses, asking people to rate the importance of a variety of economic and social issues facing the country. At the end of the questionnaire is an (optional) invitation to donate money to the organization. Which of the following statements about this survey is true?
A) The survey results are invalid because it’s impossible to word questions about politics without creating bias.

B) The survey results are invalid because only surveys conducted by phone are free from bias.

C) The survey results will underestimate support for this political action committee in the entire population because people who respond are less likely to support an organization that asks for money.

D) The survey results will overestimate support for this political action committee in the entire population because people more likely to respond if they are prepared to donate money.

E) Since the survey was sent to randomly-selected households, it should be free of bias.