You Want to Know Whether Cookies Made with Unbleached Flour

Multiple Choice

You want to know whether cookies made with unbleached flour taste better than cookies made with bleached flour; which of the following has the strongest experimental design to test this question?

A) Make two batches of cookies, both with bleached flour; one taster tries both types and ranks which type he likes best.
B) Make two batches of cookies, one with bleached flour and one with unbleached flour; one taster tries both types and ranks which type he likes best.
C) Make two batches of cookies, one with bleached flour and one with unbleached flour; twenty tasters try both types and rank which type they like best.
D) Make two batches of cookies, one with bleached flour and one with unbleached flour; twenty tasters try both types without knowing which ones they are eating and rank which type they like best.