Explain whether each of the following is a positive or negative externality.

smoking on campus exposes students to secondhand smoke.

• college graduates add to the nation's supply of skilled workers and add to productivity.

• biotech firms invent new medicines.

• using energy-saving light bulbs reduces the pollution from electricity-generating plants.

• crowded freeways with heavy truck usage expose the surrounding communities to increased health risks.

• restoring the amazon forest can reduce global levels of pollution.