oxygen-rich and oxygen-poor blood never mix

A) fish circulatory system
B) amphibian circulatory system
C) ​mammalian circulatory system

Oxygen-rich

Describes an environment or substance containing high levels of oxygen, often associated with well-oxygenated blood and atmospheres conducive to aerobic life forms.

Oxygen-poor

A condition or environment where the concentration of oxygen is significantly lower than the average.

Circulatory System

The circulatory system is the body's network of organs and vessels through which blood and lymph circulate, delivering nutrients and oxygen to cells and removing waste products.