Question

the human cardiovascular system is considered closed because ____________.
a. blood is continuously circulated in the body.
b. blood provides nutrients to organs.
c. blood collects oxygen from the lungs
d. there are no holes for blood to enter or leave the system
please select the best answer from the choices provided.
a
b
c
d

Explanation:

A closed system means there are no openings for substances to enter or leave. In the human cardiovascular system, blood circulates within blood vessels (arteries, veins, capillaries) which form a closed - loop. There are no holes for blood to enter or leave the system. Option A (continuous circulation) is a characteristic of the cardiovascular system but not the reason it's called closed. Option B (providing nutrients) and Option C (collecting oxygen) are functions of the blood but not related to the system being closed.

Answer:

D. there are no holes for blood to enter or leave the system