For the following, which type of t-test is required?
(a) Studying the effects of a memory drug on Alzheimer's patients, testing a group of patients before and after administration of the drug.
(b) Studying whether men and women rate the persuasiveness of an argument delivered by a female speaker differently.
(c) The study described in part
(b), but with the added requirement that for each man of a particular age, there is a woman of the same age.