Depending on the depth of your question, I would say
1) The Heart
2) Arteries
3) Veins
a little more in depth might say
1) Heart
2) Arteries & Veins
3) Capilleries
but I'd probably go with the first three (especially if you don't know what capilleries are).
drow the three major parst of circulatory system
The Heart, The Blood, and the Blood Vessels
The circulatory system is important to humans because the main components are the heart, the blood, and blood vessels.
The three main parts of the circulatory system are the heart, blood vessels, and blood.
The components of the circulatory system include the heart, blood, and blood vessels. The pulmonary circulation is also part of this complex system.
The circulatory system is composed of vessels and muscles that control the flow of blood around the body. This process of blood flowing around the body is called circulation. The main components of the circulatory system are the heart, arteries, capillaries and the veins.
Arteries, Vessels, Veins, and your heart
the heart is the main circulatory organ of the frog
The circulatory system can be considered as composed of two parts: The main components of the human circulatory system are the heart, the blood, by tissues undergoing high metabolism, as they require increased levels of oxygen.
To circulate blood and nutrients to all the components of the body.
the veins the blood and the lungs
Veins, Heart, Arteries, Capillaries, and Arteriole