Externalities can be both negative, i.e., impose costs on some third party, or positive, i.e., confer benefits on some third party. All of the following are cited as external benefits of the September 11 attacks except: Group of answer choices the creation of the Department of Homeland Security. a decrease in the spread and severity of influenza. a decrease in crime in Washington, D.C. whenever the federal terror-alert level went up. the increase in revenues received by California farmers who increased their production of marijuana