Critical Reasoning

Politicians sometimes use focus groups to help them arrive at popular policy positions. A staffer will assemble a group of citizens and ask the members of the group about their feelings on a particular issue. The politician will then base his or her position on the consensus opinion of the focus group.

The answer to which of the following questions would be most useful in evaluating the value of focus groups to a politician?

A) Are the members of the focus group well informed about the policy issues in question?
B) Are the members of the focus group a representative sample of the voters in the politician's district?
C) Does the politician agree with the policy position supported by the focus group?
D) Does the focus group know that its responses are being used to help a politician develop a policy position?
E) Does the focus group support the politician that is relying on its opinions?

The Official Answer is B.

How can I discard the rest of the options? Can anybody explain to me option by option?