a counselor wishes to examine the benefits of a parenting class on parenting skills. he decides to administer a questionnaire to the 10 parents who have attended the most recent class. how could this study be improved? select all that apply. a) administer a questionnaire to parents who have not attended the class. b) use a random sample of all patients, who have attended the class. c) increase the sample size. d) give parents some sample responses, prior to administering the questionnaire.