Comment on the following sampling designs: a$.$ A citizen$$s group interested in generating public and finan$-$ cial support for a new university basketball arena prints a questionnaire in area newspapers. Readers return the ques$-$ tionnaires by mail. b$.$ A department store that wishes to examine whether it is losing or gaining customers draws a sample from its list of credit card holders by selecting every tenth name. c$.$ A motorcycle manufacturer decides to research consumer characteristics by sending one hundred questionnaires to each of its dealers. The dealers will then use their sales records to track down buyers of this brand of motorcycle and distribute the questionnaires