1 Which of the following is an example of a positive externality?

a Bob mows Hillary's lawn and is paid $100 for performing the service.

b While mowing the lawn, Bob's lawnmower spews out smoke that Hil lary's neighbour Kristen has to breathe.

c Hillary's newly cut lawn makes her neighbourhood more attractive.

d Hillary's neighbours pay her if she promises to get her lawn cut on a regular basis.