Which of the following is not one of the reasons that closed circulatory systems are more efficient than open circulatory systems?

• A. Closed systems rely exclusively on simple diffusion for transport, whereas open systems rely on pumping mechanisms.
• B. Transport within closed systems is more rapid than in open systems.
• C. Blood can easily be directed to specific areas in closed systems, but not in open systems.
• D. Closed systems operate better under higher pressure than do open systems.