Which of the following is not a true statement about open and closed circulatory systems? a. Both systems have some sort of a heart that pumps a circulatory fluid through the body. b. A frog has an open circulatory system; other vertebrates have closed circulatory systems. c. The blood and interstitial fluid are separate in a closed system but are indistinguishable in an open system. d. Some of the circulation of blood in both systems results from body movements.