Is it possible to make up for missed sleep on the weekends? Dr. Daniel Cohen investigated this prevalent belief by disrupting the circadian rhythms of a group of volunteers. Participants remained conscious for 33-hour stretches—equivalent to staying awake all night—and then slept for 10 hours. While the volunteers were awake, Cohen periodically tested their mental and motor skills. The sleep-deprived volunteers scored fairly well soon after waking, but as the hours wore on, the participants' ability to think clearly, as well as their reaction times, steadily worsened. The study implies that the chronically sleep-deprived may function normally for a short time but inevitably slow down, even if they attempt to catch up on their sleep. Do It!

The volunteers' performance eventually .

A stabilized
B accelerated
C intensified
D deteriorated