Which of the Following Polls Is Most Likely to Have

Multiple Choice

Which of the following polls is most likely to have the most valid results?

A) A survey regarding presidential candidate preference conducted within a discussion group in which the participants already know each other (a church group, a group culled from the same office, etc.)
B) An online poll asking about presidential candidate preference
C) An exit poll conducted one-on-one with people who have just voted in a presidential election
D) A telephone survey about presidential candidate preference that is conducted at 6 p.m. each evening for one week