Why Is an Open Circulatory System Less Efficient Than a Closed

Why is an open circulatory system less efficient than a closed circulatory system?

A) It is more difficult to quickly deliver O₂ to specific tissues when needed with an open circulatory system.
B) There is no heart to pump the blood in an open circulatory system.
C) Open circulatory systems lack respiratory pigments that bind to oxygen.
D) Metabolic wastes cannot be removed from tissues in an open circulatory system.
E) Blood cannot be used to transport nutrients in an open circulatory system.