Suppose that you borrow your friend's laptop for a week to see whether you want to purchase one yourself. The computer makes a slight whirring sound just before it shuts down automatically due to low battery power. At first you didn't notice the sound and were surprised when the computer shut down. After a few days, however, you now reach for the power cord as soon as you hear the sound. Answer the following questions based upon your knowledge of classical conditioning.In this example, what is the whirring sound?