Question

Which of the following describes a response to external stimuli?

a boy sneezes when exposed to cat dander

a girl eats food when she is hungry

a child becomes hyperactive due to a chemical imbalance

a person yawns when oxygen levels in the blood are low

Answer 1

The correct answer is A.

Hunger, chemical imbalance, and blood levels are all internal issues. Cat dander on the other hand is not something the body creates or and is something in the environment.
Thus, your answer is A.