Indicate which of the following activities create a positive externality, a negative externality, or no externality at all:

a. During a live theater performance, an audience member’s cell phone loudly rings.

b. You are given a flu shot.

c. You purchase and drink a soda during a break from class.

d. A college fraternity and sorority clean up trash along a two-mile stretch on the highway.

e. A firm dumps chemical waste into a local water reservoir.

f. The person down the hall in your dorm plays loud music while you are trying to sleep.