Scenario Two Researchers Addressed the Generally Accepted Idea That Boxer Shorts

Scenario
Two researchers addressed the generally accepted idea that boxer shorts are better for male fertility than briefs because they lower testicular temperature. They begin by saying, "Although this idea is regarded as dogma by many in the lay community and the changing of underwear type is a therapy frequently recommended by medical practitioners, there is a paucity of data measuring scrotal temperature as a function of underwear type. ("Munkelwitz, Robert, and Gilbert, Bruce R. "Are boxer shorts really better? A critical analysis of the role of underwear type in male subfertility." The Journal of Urology, 160.4 (1998) : 1329-1333.)
-Which experimental design is best to test the idea that scrotal temperature is less with boxers than with briefs?

A) Take an equal number of men wearing boxers and men wearing briefs and have them go into a clinic and have their scrotal temperatures measured.
B) Recruit a number of men of approximately the same age and have some put on boxers and some put on briefs and then measure their scrotal temperatures.
C) Recruit a number of men of approximately the same age with half wearing boxers and half wearing briefs. Have them spend time in a room of the same constant temperature and then measure their scrotal temperatures.
D) Take the first 100 men who come into a fertility clinic, record who are wearing boxers and who are wearing briefs, and then measure their scrotal temperatures.