Answer:
underprovide; overprovide
Step-by-step explanation:
A good has positive externality if the benefits to third parties not involved in production is greater than the cost. an example of an activity that generates positive externality is research and development. Due to the high cost of R & D, they are usually under-produced. Government can encourage the production of activities that generate positive externality by granting subsidies.
A good has negative externality if the costs to third parties not involved in production is greater than the benefits. an example of an activity that generates negative externality is pollution. Pollution can be generated at little or no cost, so they are usually overproduced. Government can discourage the production of activities that generate negative externality by taxation