Consider two types of cars: gasoline-powered cars and electric cars.


Because conventional gasoline-powered cars burn fuel during their operation, people who drive gasoline-powered cars impose a _______(positive/negative) externality on the society. A policy implication of this result is a ______ (tax on/subsidy for) those who drive gasoline-powered cars.


Because electric cars help reduce greenhouse gas emissions, people who drive electric cars impose a ______ (positive/negative) externality on the society. A policy implication of this result is a _______ (subsidy for/tax on) those who drive electric cars.