Betty, a cardholder, receives a call inquiring about her ssn. the caller introduces himself as an employee of the travel card vendor and tells her that he needs her ssn to verify the validity of the card. what should betty do?

"in the electricity industry, low average total costs are obtained only through large-scale production. in other words, the initial cost of setting up all the necessary wiring makes it risky and, most likely, unprofitable for competitors to enter the market. throughout much of the 20th century, many people viewed south africa’s de beers group as a monopoly because it controlled a large percentage of diamond production and sales. patents are granted to inventors of a product or process for a certain number of years. the reason for this is to encourage innovation in the economy. without the existence of patents, it is argued, research and development for improved electronics is unlikely to take place, since there’s nothing preventing another firm from stealing the idea, copying the product, and producing it without incurring the devel opment costs."which of the following best explains the barriers to entry that exist in this scenario? increasing returns to scale legal barriers exclusive ownership of a necessary resource