Alan Is Sitting in a Bar Drinking Beers That Cost

Alan is sitting in a bar drinking beers that cost $4 each. According to the economic decision rule, Alan will stop drinking when the marginal:

A) benefit to him of an additional beer is less than $4.
B) cost to him of an additional beer is less than the marginal benefit.
C) cost remains at $4.
D) benefit to him of an additional beer is greater than $4.