18a.[3] Give an example of a negative externality that is an effect of some consumers' actions on the productivity of certain firms. [ 1 point extra if your example is the externality with the most damage, billions of dollars in damage per year.] b.[2] Give an example of a positive externality that is an effect of some consumers' actions on other consumers' welfare, an effect that the affected consumers do not pay for. [ 2 points extra if you describe the externality with the highest estimated market value, worth trillions of dollars per year in the US.]