单项选择题

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Although "lie detectors" are widely used by governments, police departments and businesses, the results are not always accurate. Lie detectors are commonly (26) as emotion detectors, for their aim is to (27) bodily changes that contradict what a (28) says. The lie detector records changes (29) heart rate, breathing, blood pressure, and the electrical (30) of the skin. In the first part of the (31) you are electronically connected to the machine and (32) a few neutral questions ("What is your name" etc. ). Your physical reactions serve (33) the standard for evaluating what comes (34) Then you are presented with a few (35) questions among the neutral ones ( "When did you rob the bank" ). The idea is that if you are (36) , your body will reveal the truth, even if you try to (37) it. Your heart rate and breathing will change (38) as you respond to the questions.
That is the theory, but psychologists have found that lie detectors are simply not (39) . Since most physical changes are the same across (40) emotions, lie detectors cannot tell (41) you are feeling angry, nervous or excited. (42) people may be tense and nervous (43) the whole procedure. They may react physiologically to a certain word ( "bank" ) not because they robbed it, but because they recently used a bad check. In either (44) , the machine will record a "lie".
On the other hand, some practiced liars can lie (45) hesitation, so the reverse mistake is also common.