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题库 / GMATLA-CR-73
Which of the following most logically completes the passage?
Appendicitis (inflammation of the appendix) is potentially fatal; consequently, patients with symptoms strongly suggesting appendicitis almost always have their appendix removed. The appropriate surgery is low-risk but performed unnecessarily in about 20 percent of all cases. A newly developed internal scan for appendicitis is highly accurate, producing two misdiagnoses for every 98 correct diagnoses. Clearly, using this test, doctors can largely avoid unnecessary removals of the appendix without, however, performing any fewer necessary ones than before, since ______.
the patients who are correctly diagnosed with this test as not having appendicitis invariably have medical conditions that are much less serious than appendicitis
the misdiagnoses produced by this test are always instances of attributing appendicitis to someone who does not, in fact, have it
all of the patients who are diagnosed with this test as having appendicitis do, in fact, have appendicitis
every patient who is diagnosed with this test as having appendicitis has more than one of the symptoms generally associated with appendicitis
the only patients who are misdiagnosed using this test are patients who lack one or more of the symptoms that are generally associated with appendicitis
误诊就两种，有病诊断成没病，和没病诊断成有病。
1. 如果是有病诊断成没病，这个问题比较大，减少了医生的necessary removals。
2. 如果是没病诊断成有病，属于unnecessary removals。
问题问的是可以减少unnecessary removal，不减少necessary removal的原因。
如果新的诊疗手段不犯下第一种错误，同时犯第二种错误的几率大幅减小，那么就可以达到问题的所要求的标准了。
因此B的含义是，新的手段只犯第二种错误，再加上98%的正确率，那么就符合问题的标准了。
C的意思是：
所有被诊断出有病的人都是有病的，但是如果被诊断出没病的人当中也有有病的人，那么还是犯了第一种错误，减少了了necessary removals.
好答案
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