When External Costs Result from the Production of a Good

When external costs result from the production of a good,

A) Producers have an incentive to produce too little.
B) Consumers have an incentive to consume too little.
C) Both producers and consumers have an incentive to produce and consume too much.
D) Producers and consumers are not affecteD.If a product yields external costs,the social demand is less than the market demand.