5. Which of the following is a horizontal practice subject to antitrust scrutiny? a. A manufa

5. Which of the following is a horizontal practice subject to antitrust scrutiny?
       a. A manufacturer of flight navigation system requires retailers to sell at a price it specifies.
      b. A manufacturer of flight communication system grants exclusive rights to a distributing            firm.   
    c. Navigation system manufacturers of U.S. refuse to sell critical parts to a leading  aircraft manufacturer. 
       d. Two aircraft manufacturers announce a merger that would create a monopoly in the national     aircraft manufacturing industry.