Until a century ago, bloodletting was used to treat many ailments. Dating back to before thetime of Christ, the treatment involves letting a type of worm, called a leech, suck blood from thepatient. People believed that there were liquids called humors in the body and that these determineda person’s personality and health. Bloodletting, they thought, restored a balance to these humors. 　　At the time, little was known of the workings of the human body, but people did know that thesame liquid, blood, flowed throughout everyone’s body. They knew it was a vital substance, for lossof any great amount of it meant certain death. Thus, they concluded that all diseases were carried inthe bloodstream, and that if the body was relieved of bad blood, health would return. Bloodletting,however, came to be use as cure-all. Women were bled to keep them from blushing, while membersof the clergy were bled to prevent them from thinking sinful and worldly thoughts. 　　From the eleventh to the eighteenth centuries, barbers were the people to go to if you needed tobe bled. This custom explains the significance of the traditional barber’s pole: the white stripesstand for bandages and the red stripes for blood.
21.This passage is concerned with
(A) healthy people and doctors.
(B) bleeding as a cure-all.
(C) barbers of long ago.
(D) leeches with special jobs to do.