Mark Got Paint Stripper in His Eye and the Hospital

Multiple Choice

Mark got paint stripper in his eye and the hospital gave him morphine, so he was feeling no pain when he got home. Why was this drug most likely effective?

A) Because the brain is most accepting of novel types of chemicals
B) Because its properties resemble those of natural brain chemicals
C) Because it stimulates the brain to release its own neurochemicals
D) Because the mechanisms of opiates may involve both (b) and (c)