It would be (b.)
But really If you think about all of them they do all apply.
The difference between a positive externality and a negative externality is that the former has good effects on people while the latter has bad effects. An externality occurs when an economic action takes place and has an effect on people who are not directly part of the action.
<span>The exhibition was intended to give a preview, a glimpse of the future, of the possibilities. But not a fantastical or an improbable one but a future that is within our grasps. A future that we are actually reaching with these ideas and technologies that are in development and once mastered will change our lives immeasurably.</span>
