What is a cartel, and why is it generally considered illegal in many countries?

• A. A cartel is a group of consumers that negotiate prices with firms.
• B. A cartel is a government-regulated entity that ensures fair pricing.
• C. A cartel is a single firm that dominates a market, increasing competition.
• D. A cartel is a group of firms that collude to set prices and quantities, reducing competition.

Answer: (D)