"you are speeding down the highway and see the flashing lights of a police car in your rearview mirror. your heart begins to pound as you slow down, but the police car passes you in pursuit of someone else. your physical reaction occurs at which phase of the general adaptation syndrome? "

The general adaptation syndrome (GAS) coined by Hans Seyle refers to the expected ways in which our body responds to stress. The GAS has various phases or stages. Here we will be focusing on the alarm phase, where our fight-or-flight response becomes activated when we experience stress.This can involve a pounding heart, shallow respiration, dilated pupils etc. 

In this given situation, when you are fearful because you think the police is making you pullover, when your heart starts racing, you exhibit behavior associated with the alarm phase of the general adaptation syndrome. 

The answer is alarm stage.
During this stage, our body is filled with adrenaline and we will automatically enter fight-or-flight situation.
This will make us had a sudden outburst in energy and make our senses become more sensitive in order to stay focus on the problem at hand.