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.