Why Is Subject Selection in Survey Research Considered Nonrandom

Why is subject selection in survey research considered nonrandom?

A) If monetary reward is offered as an inducement, subjects may participate only to get the reward. The sample may include fewer people who are well-off financially.
B) There is no direct contact with the subjects.
C) Follow-up reminders make recruitment long and drawn-out.
D) Inducements are essentially manipulative; potential subjects who resent manipulation refuse to return surveys.
E) Refusal rates average 50% or more, and this makes the sample nonrepresentative.