Answer:B - Network Externality
Explanation: According to the American Economic Review by Michael Katz and Carl Shapiro in 1985 define network externality as the utility that a given user derives from a good depends upon the number of other users who are in the same network.
Understanding the above definition, goods exhibit network externality whenever the consumer enjoys benefits or suffers costs from changes in quantities demanded of a product. These benefits and costs result from such considerations as brand familiarity, compatibility, product information, status and the prices of related goods.