Over the last twenty years, consumer behavior has changed dramatically due to the ease of purchasing goods online, and Amazon has been at the center of this revolution. As a result, many traditional retailers have gone out of business and in certain areas, store vacancies have had a negative impact on property values. Moving forward, it is speculated that the use of robots by Amazon will increase productivity but slow or halt its hiring of employees as corporate expansion continues.

Based on the above, which of the following is an externality?

the use of technology by Amazon

increase in convenience for online shoppers

reduction in property values due to store vacancies

traditional retailers' bankruptcies