题目内容：
Questionsare based on the following passage．
Polygraphs, or "lie detectors", are used widely in America, including on sex offenders, but in Britain many remain skeptical．Polygraphs do not detect lies．They measure changes in physiology, such as breathing rate, sweating and blood pressure．Telling lies is often stressful and can prompt jumps
in the readings．But other things-fear, embarrassment, worries about being wrongfully accused-can do the same．Enthusiasts say that polygraphs accurately detect lies 80 - 90% of the time．The British Psychological Society cites studies showing similar figures but cautions that problems in the research mean that the real rate is probably much lower．And "false positive" rates ( defming a truthful pemon a liar) can be as high as 47%．
Boosters of the government's scheme say the point is that using polygraphs encourages sex offenders to reveal more information, before, during and after the test．In a 2010 -2011 pilot study offenders who took polygraph tests made more than twice as many "clinically significant exposures"-- information that could prompt changes in the way they are managed--as those that did not．Many said they would not have done so without undergoing the test．Jane Wood, a psychologist at the University of Kent who co-authored the report on the pilot, says that some offenders found the tests helpful as way to convince their families they were being honest about their behaviour．Others said that the discussions prompted when they failed the test helped them better to understand the conditions of their license．Polygraph tests do not stand on their own, argues Don Grubin, a professor of psychiatry atNewcastle University; they should be one of a number of tools used to assess offenders．Nonetheless some remain uneasy．Those using the tests may become contented, worries Anne McAlinden of Queen's University, Belfast, and give them excessive weight．In the government's study, the more tests offenders took, the fewer lies were labeled．That might indicate that they became more truthful, or it might suggest that they were getting better at gaming the test．
Which of the following statements about polygraphs is tree?______ A．They are widely used and trusted by Americans as well as the British．
B．They test psychological changes, such as fear, embarrassment and worries．
C．They are proved to be able to detet lies as accurately high as 80 -90% of the time．
D．They may not be as reliable as enthusiasts have advocated．
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