Which of the Following Is the Best Example of a Vertically

Which of the following is the best example of a vertically integrated firm?

A) General Electric, which produces light bulbs, jet engines, and washing machines
B) Kinko's, which has a photocopy store near many colleges and universities
C) USX Corporation, which owns ore and coal mines, coke ovens, blast furnaces, mills, and foundries
D) Intel, which makes computer chips for most computer manufacturers
E) Century 21, which has real estate offices that help people sell a house in one city and buy another house in another city