First one
The fight or flight response is a “response to an acute threat to survival that is marked by physical changes, including nervous and endocrine changes, that prepare a human or an animal to react or to retreat” (Britannica, 2019). In other words, it is what our body does when encountering a threat. Below, we will discuss what sorts of threats this phenomenon is triggered by, the specific nervous and endocrine changes referred to in this definition, and how the term “fight or flight” is an oversimplification.