Question

People whose bodies cannot produce the substance cytochrome P450 are three times as likely to develop Parkinson's disease, a disease that affects the brain, as are people whose bodies do produce this substance. Since cytochrome P450 protects the brain from toxic chemicals, toxic chemicals probably play a role in the development of Parkinson's disease.
Which of the following, if true, most strongly supports the argument?

• A. It will soon be possible for cytochrome P450 to be synthesized for the treatment of people whose bodies cannot produce this substance.
• B. Many people whose bodies are unable to produce cytochrome P450 lack the ability to produce certain other substances as well.
• C. Cytochrome P450 has no effect on the brain other than to protect it from toxic chemicals.
• D. People with Parkinson's disease often exhibit a marked lessening in the severity of their symptoms when they are treated with dopamine, a chemical produced naturally in the brain.
• E. Many people with Parkinson's disease have the ability to produce cytochrome P450 naturally.

Hint:

A powerful way to strengthen a causal argument is to eliminate alternative explanations. If the argument claims A causes C because of mechanism B, the argument is stronger if you can show that A is not linked to C through any other mechanism.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This is a "strengthen the argument" question. We need to identify the conclusion and the evidence, find the logical gap or assumption, and then select the answer choice that best supports that assumption.
Step 2: Detailed Explanation:
Argument Breakdown: \begin{itemize} \item Premise 1 (Correlation): Lack of cytochrome P450 is correlated with a much higher risk of Parkinson's. \item Premise 2 (Function): The function of cytochrome P450 is to protect the brain from toxins. \item Conclusion (Causation): Therefore, toxins are a probable cause of Parkinson's. \end{itemize} The logical leap/assumption: The argument assumes that the only relevant role P450 plays is its stated function of protecting against toxins. If P450 had other functions, its absence might cause Parkinson's through a different mechanism, and the conclusion about toxins would be weakened. To strengthen the argument, we should reinforce the idea that the toxin-protection function is the key link.
Evaluate the options: \begin{itemize} \item (A) A potential future treatment does not provide evidence about the cause of the disease. \item (B) This weakens the argument. If people lacking P450 also lack other substances, it introduces alternative causes. Perhaps the lack of one of those other substances is what leads to Parkinson's, not the exposure to toxins. \item (C) This strongly supports the argument. By stating that P450 has no other effect on the brain, it eliminates alternative causal pathways. It isolates the toxin-protection function as the only way that the presence or absence of P450 could affect the brain. This makes it much more likely that the correlation between lack of P450 and Parkinson's is due to the increased damage from toxins. \item (D) Information about a treatment for symptoms (dopamine) is irrelevant to the initial cause of the disease. \item (E) This slightly weakens the argument by showing that having P450 doesn't guarantee prevention of Parkinson's, suggesting other causes are involved. While it doesn't destroy the argument, it certainly doesn't strengthen it. \end{itemize} Step 3: Final Answer:
By ruling out other possible functions of cytochrome P450, option (C) strengthens the argument that its role in protecting against toxic chemicals is the reason its absence is linked to Parkinson's disease.