Given the task definition and input, reply with output. In this task you are given a short story and a question regarding that story. You must answer the question based on the events of the story. Try to use the same words in the story to answer each question. You should completely answer the question in a short answer. Do not include information that is unnecessary to answer the question.

It was 4 AM. Amy, Kim and Lynn had been up all night. They had an evening full of adventure. And they were still wide awake. Amy realized it was probably the adrenaline making them so alert.
Why did Amy realize it was probably the adrenaline making them so alert?
Amy, Kim and Lynn were fully alert.