Which of the Following Best Illustrates an Externality

Which of the following best illustrates an externality?

A) A worker agrees to work in a dangerous job because it is the best job the worker can get .
B) A job is so dangerous that the employer cannot attract workers, resulting in a good not being produced despite the fact that it is valued by consumers.
C) Parents, weighing the costs and benefits to their child of going to school versus working, choose to make the child work in a local factory.
D) An employer and worker agree to produce a good with a production method that emits pollutions on the nearby community