题目内容：
阅读材料，回答题。The Chinese have used a method called acupuncture (针灸) to perform operations for about4,000 years without putting the patient to sleep. This involves placing flexible needles into certain parts of the body. The needles are available in a number of stores in China and anyone may buy them. To learn how to use the needles takes about one month of training. But to be skillful requires greater time. The person who performs the acupuncture knows how to put in the needles so the needles themselves are not painful. This person also knows where to place the needles so the patient feels no pain in the area where the operation is to be performed. A particular operation might require 25 or more needles placed in various parts of the body. But now this operation requires only 3 or 4 needles.
Today, the Chinese doctors are trying to learn more about acupuncture. They are trying to develop a convincing theory to explain how the needles work in preventing pain, or why a needle in the wrist, for example, would prevent the pain in the area of the mouth.
A patient who needs an operation is given a choice between having acupuncture or having one of the chemicals used for putting him to sleep. It has been estimated that over half of the patients choose acupuncture because there is no sickness after the operation but the chemical may make the patient sick for a few hours or a day.
Acupuncture is_______ A．a medical operation
B．a medical needle
C．a medical technique
D．a medical machine
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