It Is Very Common for Magazines to Conduct Surveys in Which

It is very common for magazines to conduct surveys in which readers voluntarily fill out survey cards and mail the cards to the publisher.The main problem with conducting a survey in this manner is that

A) some of these surveys will be lost by the postal service.
B) people are not truthful when filling out anonymous surveys.
C) mail-in surveys are generally not as effective as surveys conducted over the Internet.
D) people who respond to the survey are likely to be different from those who do not respond.