Final answer:
During the first stage of sleep, the body transitions from wakefulness to sleep with decreased heartbeat and respiration rates, reduced muscle tension and body temperature, and a shift from alpha to theta brain wave activity.
Step-by-step explanation:
The body's typical state during the first stage of sleep is not characterized by increased physical activity, deep REM patterns, or a state of complete rest with no physiological activity. Instead, the correct answer is C. The body is in a transitional state between wakefulness and sleep during the first stage of sleep. During this stage, known as stage 1 sleep, there is a slowdown in both the rates of respiration and heartbeat, a decrease in muscle tension, and a reduction in core body temperature. Brain wave activity slows down and transitions from alpha waves (which closely resemble the patterns observed in a relaxed but awake person) to theta waves, characterized by even lower frequency and higher amplitude.