Identify one common symptom of shock.

A rapid heartbeat, or tachycardia, is a common symptom of shock because the body is responding to a perceived or actual deficiency in blood flow or oxygenation to tissues. When an individual is experiencing shock, the body's compensatory mechanisms kick in to maintain vital organ function. One of the primary responses is to increase the heart rate, thereby trying to deliver more oxygenated blood to essential organs. This increase in heart rate is a clear signal that the body is under stress, often due to factors such as blood loss, dehydration, or severe infection.

The other options represent symptoms that may not directly correlate with the typical physiological response seen in shock. For instance, a slow heartbeat is not a common symptom, as it indicates a different type of cardiac response that does not align with the body's need to compensate for shock. Similarly, while drowsiness can occur in severe cases due to lack of perfusion or oxygenation, it is not as immediate or characteristic as the rapid heartbeat. Flushed skin may suggest other conditions related to fever or an allergic reaction rather than shock specifically. Thus, the rapid heartbeat stands out as a clear and typical manifestation of shock.