Phlebotomy Technician Practice Exam (NCPT/CPT)

Veins are the blood vessels responsible for carrying blood back to the heart. While arteries carry blood away from the heart, they do not contain valves. Capillaries are the smallest blood vessels that allow for exchange of nutrients and waste between tissues and the blood. Chambers refer to the different sections or compartments of the heart. Thus, the correct option is B, veins, as they contain valves that prevent backflow and maintain proper blood flow direction.