Recall the Application About How Microsoft Responds to the Threat

Recall the Application about how Microsoft responds to the threat of potential competitors to answer the following question(s) .
-Recall the Application.Which of the following best represents the way Microsoft keeps other firms from entering the market?

A) Microsoft buys out small firms that have the potential to make a similar product.
B) Microsoft uses limit pricing to deter entry.
C) Microsoft has a patent that prohibits any firm from producing a similar product.
D) Microsoft is a pure monopoly where it is impossible for other firms to enter the market.