Our sleep rhythms are tied to a 24-hour day because
A. The time of peak activity is invariant from person to person.
B. They are tied to external time markers like light and dark.
C. They have adapted to technological improvements made in the last century.
D. Everyone needs at least 8 hours of sleep every night.
Answer:B
Our sleep rhythms are tied to a 24-hour day because
A. The time of peak activity is invariant from person to person. B. They are tied to external time markers like light and dark. C. They have adapted to technological improvements made in the last century. D. Everyone needs at least 8 hours of sleep every night.