Passage Summary: A doctor decides a patient didn't swallow a specific chemical because the patient lacks the skin rash that typically follows the mineral loss caused by that chemical.

Conclusion: The physician determined that Jones did not ingest the chemical in question.

Reasoning: Swallowing the chemical leads to a mineral deficiency, which in turn causes skin inflammation; because Jones showed no skin inflammation upon arrival, the physician inferred the chemical was not swallowed.

Analysis: The physician's logic relies on the assumption that the skin inflammation would appear immediately or very shortly after ingestion. To weaken this, look for an answer choice that introduces a time lag, such as the mineral deficiency taking hours to manifest or the rash taking time to develop on the skin. If the symptoms aren't instantaneous, the absence of a rash at the emergency room doesn't prove the chemical isn't currently in his system.