The answer is endocrine system because it deals with hormones around the body and is controlled by the pituitary gland.
The item from this list which isn't considered a stimulant would be alcohol - a. It is considered to be a depressant. All the other items - nicotine, caffeine, and cocaine have stimulating effects which are known to their useres, while alcohol doesn't have an stimulating effect generally.
The answer to your question will be C) because it is the only option that can contaminate something.
