Final answer:
The most likely answer to who introduces illegal drugs to student users is friends, as students typically obtain illegal substances from their peer group. The case study highlights that another student was the provider of the drugs.
Step-by-step explanation:
The question is concerned with who is most responsible for introducing illegal drugs to student users. Based on the context provided, which highlights illicit substance use among students, the most common culprit in drug-related peer scenarios is a friend. It should be noted that the involvement of individuals such as teachers or trusted members of the community in such activities would be highly irregular and legally actionable.
In the case study you provided, it appears that another student was the source of the illegal drugs, which aligns with option d. students. This is a common pattern, as students often obtain illegal drugs from within their peer group, including friends or acquaintances at school. Peer pressure and the desire to fit in or explore can influence these decisions, leading to drug use and its various associated risks.