All of the following are true of capillary/capillary bed structure and function, EXCEPT:
A. Their huge surface is ideal for efficient exchange of materials
B. Slow blood flow allows more time for exchange to take place
C. Blood pressure is constant across the entire capillary bed
D. When pre-capillary sphincters are open, metabolic needs of the tissue are high
E. They have thin walls only consisting of a tunica intima