The Classic Example of a Per Se Violation of Antitrust

The classic example of a per se violation of antitrust law is:

A) two companies agreeing to stop buying from a third company
B) a group of competitors deciding to outsource all manufacturing overseas
C) a group of 5 or more competitors agreeing to use the same supplier so they can buy things in bulk and get better prices
D) a group of competitors agreeing on the prices they will charge for their goods so as to eliminate price competition
E) none of the other choices are correct