State whether each of the following primarily causes an external cost or an external benefit. a. Fishing at a popular lakeside vacation spot: (Click to select) v b. Buying a fax machine: (Click to select) v c. Conducting research to find an AIDS vaccine: (Click to select) v d. Occupying a seat on a bench in a crowded park: (Click to select) ~ e. Littering: (Click to select) v f. Spaying or neutering your pet: (Click to select) v