Which are characteristics of mammals? Check all that apply.internal fertilizationthree-chambered heartendothermichighly developed nervous systemseveral nearly hollow bonesalways live on land

Mammals reproduce through internal fertilization, maintain a relatively constant body temperature (they are endothermic), and have highly developed nervous systems. Mammals have four-chambered hearts, not three-chambered hearts, and several nearly hollow bones are characteristic of birds. Also, some mammals live in water, so mammals do not always live on land.

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