What is the function of a linking verb

Ineed . read the passage, and choose the two (2) inferences that are most firmly based on the given information. although lie detector tests are based on a sound principle, they are not alwaysaccurate. the test is based on the fact that people become emotionally “stirred up”when they lie. the lie detector can sense physical changes that accompany suchemotional responses. but an innocent person may react emotionally to a keyquestion.thus, he or she appears to be lying when actually telling the truth. and criminals who lie often may feel no guilt about anything. they can therefore tell huge lies without showing the slightest emotional ripple on the lie detector. without an emotional response, there are no physical responses to detect. 1. criminals never feel any guilt about their crimes. 2. lie detector tests are not foolproof. 3. anyone can easily fool the lie-detector machine. 4. an emotional response by an innocent person