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

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

The human cardiovascular system is considered closed because there are no holes for blood to enter or leave the system

Explanation:

The closed circulatory system are made up of blood vessels called arteries from the heart that branch into small units called capillaries but eventually join up with other blood vessels called veins that are connected to the heart. So, blood is always confined to circulate within the blood vessels and the heart as there are no holes for blood to enter or leave the system

Thus, the human cardiovascular system is considered closed

d

Explanation:

edge

a: the sheep and waste material both release carbon into the atmosphere.