Answer: C. A snake hides under a rock on a hot day.
Explanation:
Thirst, hunger, and pathogens are internal issues (meaning inside of the body). Weather (heat) is something from the external environment that the snake is responding to (hiding). Therefore, the correct option is C.
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<em>Question: Which behavior is a response to an external stimulus?</em>
<em>A. A dog drinks to quench its thirst.</em>
<em>B. A squirrel eats when it is hungry.</em>
<em>C. A snake hides under a rock on a hot day.</em>
<em>D. A cat vomits to rid itself of pathogens.</em>
