Which pathogen that causes disease is the simplest and smallest? protozoa

bacteria

virus

fungus

Maintaining a healthy weight allows the respiratory system to work more effectively because a. oxygen is being delivered more adequately. b. the heart does not have to pump as forcefully. c. the capillaries are constricted. d. the lung capacity allows for small amounts of air.

Why do you need two different circuits of blood vessels in your body?

Will you get autism from being lonely?