In the United States, Barriers to Entry in Professional Team

In the United States, barriers to entry in professional team sports (for example, football and baseball) result from

A) the draft of college players, which grants teams exclusive signing rights to individual players.
B) long-term leases teams sign for stadiums and ballparks in major cities.
C) television contracts, which give networks the exclusive rights to broadcast games.
D) the reserve clause, which is a provision in contracts of professional athletes that require them to play for specific teams over the length of their contracts.