四、Over the past years, new psychoactive substances (NPS)have continued
to be rampant and even disguised as instant coffee or milk tea powder,
which endangers the physical and mental health of our countrymen. With
the advancement of technology, there are many different detection
methods for suspected drugs found by police officers on duty. Please
illustrate the features of the following three methods, and explain the
significance of their positive test results
(一)Color test(8 分)