28) E

The argument made in the text is that the drug legalization movement is dangerous and misguided.
To support this argument, it uses the example of only one place, Colorado USA. It states that ever since marijuana has been legalized in Colorado, the rates of murder and violent crimes have increased. It assumes that legalization of marijuana has caused the increase of violent crimes. This is a flaw. So statement A is correct.

Statement B is wrong because other substances are not mentioned in the text and are irrelevant in this case.

Statement C is correct. In order to prove a correlation between two things (legalization of marijuana and increase in rate of violent crimes), it must be proven repeatedly in different places too. In this case, the text only uses the example of Colorado. Therefore, this is a flaw.

So E is the answer.