Thinking is sharpest and memory is most accurate when people are at their daily peak in

A) melatonin secretion.
B) circadian arousal.
C) REM rebound.
D) hypnagogic sensations.

Circadian arousal refers to the body's natural rhythm of being most alert and awake during certain times of the day. This is commonly referred to as a person's "daily peak" and is typically in the morning for most individuals. Therefore, thinking is sharpest and memory is most accurate when people are at their daily peak in circadian arousal. None of the other options (melatonin secretion, REM rebound, hypnagogic sensations) have been shown to have a direct impact on cognitive ability or memory accuracy.