One feature that amphibians and humans have in common is a. the number of heart chambers. b. a complete separation of circuits for circulation. c. the number of circuits for circulation. d. a low blood pressure in the systemic circuit.

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1. Identify the key terms: Amphibians and humans both have circulatory systems, but they differ in structure and function.
2. Analyze each option: a. Amphibians typically have a three-chambered heart, whereas humans have a four-chambered heart.
3. Option b: Humans have a complete separation of pulmonary and systemic circuits, but amphibians have some mixing of oxygenated and deoxygenated blood due to their three-chambered heart.
4. Option c: Both amphibians and humans have two circuits for circulation - the pulmonary circuit (lungs) and the systemic circuit (rest of the body).
5. Conclude that the correct answer is c. the number of circuits for circulation, as both humans and amphibians have two circuits, despite differences in heart structure and separation of blood.