UNIT ONE LESSON ONE What Makes a Mammal a Mammal?

Mammals have the following characteristics: 1.They are covered with hair or fur. 2.They are warm-blooded (mean-ing their internal body temperature is maintained at a constant level regardless of external conditions). 3.They are usually born alive and relatively well-devel-oped, having grown inside the mother’s body in a special organ called a ... ................
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