Answer: Are an example of horizontal trade restraint. The correct answer is C.
Explanation:
When using horizontal trade restraint the insurance brokers are in a respectable agreement with each other. They all determine who will submit the bid so that they will minimize their competition with each other. They only do this when they are in the same market as each other. Business people at a higher level in the market may not adhere to this the horizontal trade restraint agreement.
If it was a vertical trade agreement it would be against firms or other businesses people at different levels in the same business.