答案

Negative externality describes a social phenomenon that some personal behaviour may interfere with those who are irrelevant with the move. The professors talks about an example of his own experience. In his childhood, there was a nice area of farmland in the neighbourhood, and the residents there liked it very much. But soon, the land owner decided to retire and would like to sell the farmland to a big company. The company which bought the farmland later turned the area into a factory. Not only the beautiful sceneries were ruined, the factory was also producing polluted air every day and the whole area suffered. Although the residents in the neighbourhood were not involved in the land assignment, they were all interfered by the contract. (124 words)