Answer: stimulus
The students reaction is explained by the theory of classical conditioning first coined by Ivan Pavlov. The students are conditioned to associate the doer closing with the pop quiz and respond accordingly. Pavlov used dogs and their response to ringing a bell every time their food was served, after a some conditioning the dogs would salivate at the sound of the bell regardless of whether or not food was present. The bell was the stimulus.
I believe your answer is (<span>A) justify a war to extend the borders of the United States. I hope this helps! :)
Have a great rest of the day.
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