Answer:
Covalent
Explanation:
A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms.
The answer should be C, the heart and the blood vessels.
The heart acts as a pump in the circulatory system. It pumps blood to organs and tissues all around the body. Meanwhile, the blood vessels (arteries, veins, and capillaries) help transport the blood to tissue and cells and back to the heart. Each type of blood vessel has their own function.
The brain is not involved in this system, as the whole circulation process does not require any us to make any decision.
In addition, there's also one structure that is in the blood vessels, but technically not another item for the circulatory system. That's valves, they are like flaps that ensure blood flowing in one wag direction and to prevent the back flow of blood.
So, the answer is C.
The rocky upper layer of the solid earth is called the "lithosphere". This rocky part includes the brittle upper portion of the mantle and also of the crust. It is bounded by the atmosphere above and of the asthenosphere which is another part of the upper portion of the mantle.
