A medical journal used a questionnaire survey to determine whether a particular ... ...

Which one of the following, if it were determined to be true, would provide the best evidence that the journal’s decision will have the desired effect?
(A) Of the readers who received questionnaires, 90 percent returned them.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Nova Press: Set F - Classification Practice