Answer:
a. True
Explanation:
Endothelial cells
These cells are found in all the parts of the circulatory system , these are about a cell thick , and composes a wall known as the edothelium , which lines all the blood vessels , i.e. , the arterioles , veins , capillaries , arteries , venules .
Beneath the endothelial cells , there is a layer of smooth muscle cells .
