What is an externality? a- a shared good or service for which it would be impractical to make consumers pay individually and to exclude nonpayers b- someone who wouldn't choose to pay for a certain good or service but who'd get the benefits of it anyway if provided as a public good c- a side effect of a good or service generating benefits or costs to someone who doesn't decide how much to produce or consume d- someone who would choose to pay for a certain good or service but does not get the benefits of it if provided as a public good