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

d

Step-by-step explanation:

Answer 2

D. Organs and muscles require more blood under stress.

Step-by-step explanation:

Because muscular contractions can have a protracted metabolic expenditure because it has to be adjusted to the demands of the contracting muscles.