Four married couples bought tickets for eight seats in a row for a football game.
a. In how many different ways can they be seated?
b. In how many ways can they be seated if each couple is to sit together with the husband to the left of his wife?
c. In how many ways can they be seated if each couple is to sit together?
d. In how many ways can they be seated if all the men are to sit together and all the women are to sit together?