PrepTest 126, Section 3, Question 7
Scientist: In our study, chemical R did not(50 more words not shown)
Which one of the following(23 more words not shown)
- AIt is cited(12 more words not shown)
- BIt is advanced(16 more words not shown)
- CIt illustrates the(25 more words not shown)
- DIt is used(16 more words not shown)
- EIt is cited(14 more words not shown)
Reading the argument
I'm with the scientist: “It didn't cause cancer in these rats” doesn't establish “It's safe for humans.”
Even before the human comparison, I'd want to know how long the study lasted. Imagine a substance whose effects take years to appear being tested for only a short time. A clean result during that window wouldn't settle its long-term effects. And moving from rats to people introduces another question: could humans respond differently? Safety would also involve more than just cancer.
The scientist develops the time issue. Some substances that cause cancer in humans don't cause it in rats, probably because the relevant exposure takes longer than the rats' short lives allow. That gives us a sensible reason not to treat this result as a guarantee of human safety.
What we’re looking for
The role question points back to the initial study result. Ask what the scientist does with it: acknowledges it, then explains why it isn't enough for a particular conclusion. The result isn't proof that the chemical is dangerous. It's a result whose limits the scientist wants us to recognize.
Working the answers
- A
Evidence that a chemical is unsafe would count against the conclusion that it is safe. But no cancer appearing in rats isn't presented as evidence of danger. The scientist says that result is insufficient to establish safety. Failing to prove a claim and supplying evidence against it are different.
- B
The scientist doesn't conclude that results from laboratory rats can never be applied to humans. The point is narrower: this no-cancer result doesn't establish that chemical R is safe. B turns a warning about what one finding can support into a blanket restriction on using rat-test results.
- C
The scientist offers short lives as a probable explanation for why some known human carcinogens cause no cancer in rats. But we haven't established that chemical R is one of those human carcinogens. Its no-cancer result doesn't itself demonstrate that short lives prevented an effect, or that rats are categorically unsuitable for such tests.
- D
We aren't told that chemical R causes cancer in humans through long-term exposure. That remains a possibility the study hasn't ruled out. The scientist's conclusion is about what we cannot establish, not a positive finding that chemical R causes human cancer.
- ECorrect
The study result is cited as insufficient to establish human safety. We can accept that chemical R caused no cancer in the laboratory rats and still withhold the conclusion that it's safe for people. E captures exactly how the scientist treats that fact.
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