Indicate whether the following activities create a positive or negative externality:

a. Late-night road construction begins on a new bridge. As a consequence, traffi c is rerouted past your house while the construction takes place.

b. An excavating company pollutes a local stream with acid rock.

c. A homeowner whose property backs up on a city park enjoys the sound of kids playing soccer.

d. A student uses her cell phone discreetly during class.

e. You and your friends volunteer to plant wildfl owers along the local highway.