6. Which of the following portrays horizontal price fixing arrangement subject to antitrust scrutiny

6. Which of the following portrays horizontal price fixing arrangement subject to antitrust scrutiny?
a. Three manufacturers with a large market share for printed circuit for cell phones agree to    control the prices in the industry.
 b. A cell phone hardware manufacturer requires dealers to carry only its parts.
c. A leading cell phone manufacturer requires retailers to sell at the price specified by the    company. d. Two manufacturers of printed circuit for cell phones announce a merger that would create a    monopoly in the industry