根据以下材料，回答题 The Chinese have used a method called acupuncture(针灸) toperform operations for about 4,000 years without putting the patient to sleep.This involves placing flexible needles (针) into certainparts of the body. The needles used are available in a number of stores inChina and everyone may buy them. To learn how to use needle takes about onemonth of training. But to be skillful requires greater time. The person whoperforms the acupuncture knows how to put in the needles so the needles themselvesare not painful. This person also knows where to place the needles so thepatient feels no pain in the area where the operation is to be performed. Theneedles are not necessarily inserted near the place where the pain is to beprevented. In the past, a particular operation might require 25 or more needlesplaced in various parts of the body. But now this operation requires only 3 or4 needles. Today the Chinese doctors are trying tolearn more about acupuncture. They are trying to develop a convincing theory toexplain 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 achoice between having acupuncture or having one of the chemicals used forputting him to sleep. It has been estimated that over half of the patients chooseacupuncture because there is no sickness after the operation whereas (然而，反之) the chemical maymake the patient sick for a few hours or a day. To learn how to use the needles, ittakes a person ______查看材料
A.several months B.a couple of weeks C.a life time D.almost one month