Reading comprehension
A polygraph machine, also known as a “lie detector,” is a common part of criminal investigations. The instrument isused to measure   31    a person’s body reacts to questions. The theory underlying it is that lying is stressful, and thatthis stress can be measured and recorded on a polygraph machine.
When a person takes a polygraph test, four to six wires, called sensors, are   32   to different parts of his body. Thesensors pick up signals from the person’s blood pressure, pulse, and perspiration.   33              the process of questioning,all the signals are recorded on a single strip of moving paper. Once the questions are finished, the examiner analyzesthe results to determine if the person tested   34    truthful.Well-trained examiners can usually detect lying with a high degree of   35    when they use a polygraph. However,because different people   36   differently when lying, a polygraph test is by no means perfect.
【題組】31.
(A) what
(B) when
(C) how
(D) why