Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children. Elementary school nurses in Renston report that the proportion of schoolchildren sent to them for treatment of allergic reactions to those chemicals has increased significantly over the past ten years. Therefore, either Renston�s schoolchildren have been exposed to greater quantities of the chemicals, or they are more sensitive to them than schoolchildren were ten years ago.
Which of the following is an assumption on which the argument depends?
A. The number of school nurses employed by Renston�s elementary schools has not decreased over the past ten years. Out of scope. Has no affect on the proportion of children sent to the nurse.
B. Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances. Out of scope. The argument isn't about other substances.
C. Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago. Correct. The argument assumes that there were no other reasons that the children were sent to the nurse. Also, this answer choice fails the negation test. Negated, this answer says that the children with the allergies were more likely to be sent to the nurse. If the children were more likely to be sent to the nurse for other reasons, we can't know for a fact that the chemicals were to blame.
D. The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston. Out of scope. The argument is not about where the children were exposed to the chemicals. Remember: the assumption is an answer choice that MUST BE TRUE for the argument to hold together. Why would it have to be true that the chemicals were not commonly used in the homes of the children?
E. Children attending elementary school do not make up a larger proportion of Renston�s population now than they did ten years ago. Not the assumption. The argument is not comparing the elementary school children to the the rest of the population. It is comparing comparing elementary school children with the allergies to elementary school children without the allergies. How the elementary school children relate to the whole population is irrelevant.
The correct answer is C. It is the only answer choice that must be true for the argument to hold together.
Remember: the assumption is an answer choice that MUST BE TRUE for the argument to hold together. If an answer choice doesn't have to be true, eliminate it.
(A useful test for assumption questions is the negation test. When you negate the correct answer choice -- when you make the answer say the opposite of what it says -- the argument will fall apart. How does this help us? Because if the argument falls apart when the answer choice is negated, then the answer choice must be true for the argument to hold together. And the assumption is exactly that: the thing that must be true for the argument to hold together. Any answer choice that fails this test can be eliminated.)
Hope this helps!
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