Which blood vessels carry oxygenated blood from the lungs to the heart?

Arteries are best defined as vessels that:

Identify $A, B$ and $C$ in the given diagram.

Which of the following has the largest total surface area in the circulatory system?

This layer is more thickened in an artery than in a vein,so the lumen is small in an artery.

Assertion : When there is a fall in the blood pressure due to loss of blood volume,this is compensated by vasoconstriction of veins.
Reason : Veins hold the extra amount of blood which can be shifted to the arteries as required.