Answer:
A. horizontal agreement in violation of the Sherman Act.
Step-by-step explanation:
According to the Sherman Antitrust Act of 1890 it restricted the activities related to interstate commerce and the competition arise in the market place
The horizontal agreement is an agreement which is done between the business who are competing with each other in order to modify the competition for all the available competitors in the market
Therefore according to the given situation, the correct option is A.