Answer:
D.Moral codes and social sanctions
Step-by-step explanation:
Hilary smoked a cigarette and she thought of throwing the cigarette butt onto her neighbor Edison's driveway. She decides to carry it to a trash can because she doesn't want to embarrass herself by letting people see her littering.
Asides from not wanting to embarrass herself , the private solutions to the externality of this action of changing her mind to trash the cigarette butt is also by knowing that littering the environment is morally wrong and defaulting will lead to some form of punishment or fine.