Which blood vessels carry oxygen and nutrients directly to the individual cells in tissues and organs?
A. Veins
B. Arteries
C. Capillaries
D. Venules

How do capillaries differ in structure from arteries and veins?

A. Capillaries have smoother muscle tissue than veins.
B. Capillaries appear to have a larger diameter than veins
C. Capillaries have valves which are absent in arteries.
D. Capillaries are only one cell thick and lack smooth muscle.