My roommate ________. This is an example of an external benefit.

A) sings (badly) in my presence
B) plays the drums whenever I am home
C) smokes cigars in the kitchen whenever I make dinner
D) cleans up after his dog and keeps it from eating my ferrets

An external benefit occurs when a third party gains a benefit from an action they are not directly involved in. In this case, the roommate cleaning up after his dog and ensuring it doesn't harm the ferrets is an external benefit to the ferrets' owner, as it reduces potential harm or inconvenience without direct involvement or effort from the ferret owner. Choices A, B, and C describe actions that are more likely to be considered nuisances or external costs rather than benefits.