PrepTest 139, Section 1, Question 3
A study of the dietary habits of a(90 more words not shown)
Of the following, which one(10 more words not shown)
- AThe argument fails(19 more words not shown)
- BThe argument neglects(13 more words not shown)
- CThe argument focuses(22 more words not shown)
- DThe argument overlooks(10 more words not shown)
- EThe argument does(12 more words not shown)
Reading the argument
What if the cancer came first?
The two groups ate similar amounts of yogurt, but the people with cancer had too little of the enzyme needed to process its galactose. The author treats that combination as evidence that unprocessed galactose caused their cancer. We haven't been told which problem came first.
Imagine cancer lowering the enzyme level. A person could then have trouble processing galactose because they already had cancer. We'd observe the same pairing of cancer and inadequate processing, without that pairing showing that galactose caused the cancer.
There are other possibilities, too. Some underlying condition might affect enzyme levels and also increase cancer risk. The useful question is why these features occur together. Simply finding them together doesn't settle the explanation.
What we’re looking for
We're asked for the strongest objection to the reasoning. My prediction is that the author may have the direction backward: low enzyme levels could be an effect of cancer instead of a step that leads to it.
Working the answers
- A
Other dietary differences could matter if they helped explain why one group developed cancer. We shouldn't dismiss that possibility. But A asks broadly whether everyone's diet matched in every other respect, without identifying a difference relevant to cancer or explaining the low enzyme levels. D offers a much more direct alternative explanation for the very relationship the author uses as evidence.
- B
An argument about what causes cancer doesn't have to give dietary advice. Before recommending that anyone avoid yogurt, we'd still need to assess whether the claimed causal relationship has been established. Failing to add a recommendation doesn't expose the mistake in that reasoning.
- C
Investigating one possible cause doesn't require an argument to discuss every other possible cause. The author doesn't say galactose is the only substance that could increase cancer risk. The problem is the evidence for this particular causal claim, not the decision to focus on it.
- DCorrect
Cancer might cause the enzyme levels to fall. Then the inability to process the galactose could be a consequence of cancer, rather than evidence that excess galactose caused it. This possibility leaves the study's observations intact while showing that the author's explanation isn't the only one. It undermines the conclusion without proving that galactose cannot be carcinogenic.
- E
The relevant fact is that the enzyme levels were too low to process the amount of galactose consumed. They don't need to be zero for that problem to arise. Knowing whether someone had no enzyme at all would still leave our central question: did inadequate processing contribute to cancer, or did cancer cause the inadequate processing?
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