This graph represents the tobacco industry.

a$.$ Does this industry create a positive or negative externality? ACCORDING TO THIS GRAPH, is the externality caused by production or consumption?

b$.$ Without government intervention, what is the expected market outcome if consumers and producers only act in their own best interest?

c$.$ What is the socially optimal price and quantity?

d$.$ Does the market overproduce or underproduce the good compared to socially optimum outcome?