If a firm becomes a monopoly, what happens to its market share and the industry's HHI?

• A. The firm's market share decreases, and the HHI decreases.
• B. The firm's market share remains the same, and the HHI remains unchanged.
• C. The firm's market share becomes 50%, and the HHI is halved.
• D. The firm's market share becomes 100%, and the HHI reaches its maximum value.

Answer: (D)