Which of the following describes a response to external stimuli

A. a person yawns when oxygen levels in the blood are low

B. a child becomes hyperactive due to a chemical imbalance

C. a boy sneezes when exposed to cat dander

D. A girl eats food when she is hungry

what about it?

is this a ?

phosphorus cycle

explanation:

the phosphorus cycle is the way that compounds of the element phosphorus, an essential nutrient, are recycled in the environment. plants absorb phosphorus compounds from the soil, and decaying organic matter, including both plant matter and animal droppings, returns it to the soil. phosphorus is a vital part of atp, the energy currency of all cells, and is vital to all forms of life.