​A rain barrel is a container that captures and stores rainwater for landscape and garden use during dry periods. As a result, rain barrels benefit the community through water conservation. If homeowners do not consider this external benefit of rain barrels, then a. ​the socially optimal quantity of rain barrels will be larger than the equilibrium quantity of rain barrels. b. ​the socially optimal quantity of rain barrels will be smaller than the equilibrium quantity of rain barrels. c. ​the socially optimal price of rain barrels will be lower than the equilibrium price of rain barrels. d. the market for rain barrels would benefit from a tax on rain barrels.