Final answer:
The correct set of opiates includes Morphine, codeine, and heroin, as these are either derived from the opium poppy or are synthetic versions that mimic natural opiates in their pain-relieving effects.
Step-by-step explanation:
The set that contains only opiates is the one that includes drugs derived from the opium poppy plant or synthetic versions of such drugs. The correct set from the provided options would be Morphine, codeine, and heroin, as all these are opiate drugs. Morphine and codeine are obtained directly from the opium poppy and used as painkillers, while heroin is a semisynthetic derivative of morphine, which is more potent. Drugs such as Oxycodone are also derived from opium and used to relieve moderate to severe pain. All of these substances act by attaching to opioid receptors in the brain, spinal cord, and gastrointestinal tract, altering the perception of pain.