Which of the following generate the type of externality previously described? Check all that apply. Your roommate Crystal has bought a puppy that barks all day while you are trying to study economics. Tim has planted several trees in his backyard that increase the beauty of the neighborhood, especially during the fall foliage season. A microbiology lab has published its breakthrough in swine flu research. The local airport has doubled the number of runways, causing additional noise pollution for the surrounding residents.