Question

Why does the heart automatically adjust the flow of blood to match activity levels?

A.
Extreme activity damages blood cells and the body needs replacements.
B.
The heart requires more oxygen when exercising.
C.
It reduces the level of oxygen in the blood.
D.
Organs and muscles require more blood under stress.

Answer 1

The heart automatically adjusts the blood flow because organs and muscles require more blood under stress.

Option D