Anyone really good at biology can solve biology question ​

What did hunter gathers do to alter the environment?

Drag each tile to the correct box. the body monitors the levels of oxygen in the blood to regulate breathing. isabel is running in a marathon and is near the finish line. she feels out of breath. how will her nervous system work to generate a reaction? arrange the tiles in chronological order. isabel's breathing rate increases. sensory receptors in the arteries detect low oxygen levels. the brain sends signals through motor neurons. sensory neurons generate an impulse. the central nervous system relays an impulse to certain brain regions.

There are fewer than 100 naturally occurring elements in the universe, but there are millions of different unified substances. explain how this can be true.