The Prime Minister of the Tiny Island Nation of Wowza

The prime minister of the tiny island nation of Wowza has proposed that the Wowzian Postal Service reduce mail delivery to its residents from 5 days a week to 3 days a week. Enacting this proposal would be optimal

A) only if the marginal cost of reducing the number of mail delivery days to 3 days a week falls to zero.
B) as long as the marginal benefit of reducing mail delivery to 3 days a week is just equal to or greater than the marginal cost of reducing mail delivery to 3 days a week.
C) as long as the marginal cost does not rise.
D) until the marginal benefit of this action is maximized.