Final answer:
Mammals have a four-chambered heart, not a two-chambered heart.
Step-by-step explanation:
The correct answer is a. They have a two-chambered heart.
Mammals are characterized by having a four-chambered heart, which allows for the efficient separation of oxygenated and deoxygenated blood. This adaptation is essential for their high metabolic rate, which is supported by their endothermic nature. Mammals also have lungs to facilitate respiration and a skeletal system composed of bone for support and protection. Additionally, they have an amnion, a fluid-filled membrane that surrounds and protects the developing fetus.
Learn more about Mammals and their characteristics