In some countries, a machine known as a lie detector is used to ___1___ in criminal investigation. The lie detector is used to determine ___2___ the person involved in the crime is telling the truth or ___3___.

How does such a machine work ? When a person ___4___ an untruth, certain body reactions may ___5___ . For example, his heart may ___6___ faster and his face may flush. His blood pressure may ___7___ rise and his breathing may ___8___ quicker. It is the ___9___ of the lie detector to record these reactions. Normally, the machine ___10___ record reactions which the subject has no control ___11___ , such as his blood pressure, respiration or pulse.

How reliable ___12___ these machines ? Some countries do not use lie detectors ___13___ they feel that these machines are not totally reliable. in fact, the success ___14___ of the lie detector depends greatly ___15___ the sensitivity of the machine.

The ability of the person ___16___ the test is also very important. The examiner must know specifically ___17___ kinds of questions to ask his subjects. The examiner would usually familiarize himself ___18___ the details of the case first. He then asks his subjects ___19___ that are totally unrelated ___20___ the case. The answers to these questions would ___21___ the examiner gauge what ___22___ ‘normal’ reactions of the subject ___23___ . After this, the examiner would ask questions of ___24___ kinds — those that are important to the case and those which have nothing to ___25___ with the case at all.


1. help 2. whether/if 3. not 4. tells 5. occur 6. beat 7. also 8. become 9. task/job 10. would 11. over 12. are 13. as/because 14. rate 15. on 16. conducting 17. what 18. with 19. questions 20. to 21. help 22. the 23. are 24. two 25. do

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