Over the last forty years the crime rate in the nation of Zundinia has steadily decreased. It is likely that this decrease can be at least partly attributed to the simultaneous decrease that has occurred in the amount of lead in the air and water in Zundinia, as people exposed to air or water that contains lead absorb some lead into their bodies, where it has negative impacts on their cognitive functioning.
Which of the following, if true, provides the best support for the hypothesis?
Lead in water can be absorbed into a person’s body through the person’s digestive system if the person drinks water that contains lead.
While, in Zundinia, paint that contains lead is no longer used, there is still paint that contains lead on the walls of some older buildings.
Forty years ago, a major initiative to increase quality of education in Zundinia was the start of a trend of improvement in education there that has continued to this day.
The adding of lead to gasoline meant for use in automobiles in Zundinia has been almost completely phased out over the past four decades.
In Zundinian cities in which most water is still transported via pipes containing lead, the crime rates are little changed from what they were 40 years ago.
Scott Woodbury-Stewart
Founder and Expert GMAT Focus Instructor
Solution:
We are looking for support for the following hypothesis:
Conclusion: It is likely that the decrease in the crime rate in Zundinia can be at least partly attributed to the simultaneous decrease that has occurred in the amount of lead in the air and water in Zundinia.
There is already some support for the hypothesis:
Premise: People exposed to air or water that contains lead absorb some lead into their bodies, where it has negative impacts on their cognitive functioning.
At the same time, the above premise is a general principal, rather than information that clearly connects the decrease in lead in the air and water in Zundinia with the decrease in the crime rate. Thus, information that indicates more clearly that a reduction in lead exposure is indeed what underlies the decrease in the crime rate in Zundinia would strengthen the support for the hypothesis.
Notice that the author is making the cause-and-effect claim that the steady decrease in the crime rate is being caused by the decrease that has occurred in the amount of lead in the air and water. As always, when an author makes a cause-and-effect claim, he makes the assumption that his cause and effect claim is correct and that there cannot be an alternative explanation for the pattern that he seeks to explain.
In answering this question, our job is to find an answer choice that strengthens that cause-and-effect claim, but in choosing an answer to this question, we have to be careful not to choose a choice that simply explains an aspect of the scenario described in the passage.
In choosing an answer to this question, we have to be careful not to choose a choice that simply explains an aspect of the scenario described in the passage.
(A) Lead in water can be absorbed into a person’s body through the person’s digestive system if the person drinks water that contains lead.
This choice does not add support for the hypothesis, but rather explains how lead from water gets absorbed into people’s bodies. The passage has already stated as fact that lead in water can be absorbed into people’s bodies. Explaining how it is absorbed does not strengthen the support for the hypothesis.
(B) While, in Zundinia, paint that contains lead is no longer used, there is still paint that contains lead on the walls of some older buildings.
This detail does not add support for the conclusion, as the fact that there is still lead to which people may be exposed certainly does not help to support the conclusion that a reduction in lead exposure is the reason for a decrease in the crime rate. At the same time, this choice does not affect the validity of the premise, which is the stated fact that the amount of lead in the air and water has decreased.
(C) Forty years ago, a major initiative to increase quality of education in Zundinia was the start of a trend of improvement in education there that has continued to this day.
This choice presents another change that has occurred over the past 40 years and that could underlie the decrease in the crime rate, an improvement in education. So, given what this choice says, it may be that better education rather than a reduction in environmental lead could underlie the decrease in the crime rate. Thus, by presenting a plausible alternative hypothesis, this choice weakens the support for the hypothesis presented in the passage.
(D) The adding of lead to gasoline meant for use in automobiles in Zundinia has been almost completely phased out over the past four decades.
This choice does not add support for the hypothesis, but rather explains why there is less lead in the air in Zundinia. We already know that the amount of lead in the air has decreased over the past 40 years. Explaining why it has decreased does not strengthen the support for the hypothesis.
CORRECT ANSWER(E) In Zundinian cities in which most water is still transported via pipes containing lead, the crime rates are little changed from what they were 40 years ago.
This choice strengthens the support for the hypothesis by showing what happens when we eliminate a variable, the decrease in the presence of lead.
It seems likely that, in cities in which most water is still transported via pipes containing lead, the water still contains lead. Thus, those cities do not have the variable “decrease of the amount of lead in the water.” It is also the case that in those cities the crime rates didn’t decrease.
Thus, without the variable “decrease in the amount of lead in the water” we also don’t have the result “decrease in the crime rate.” Therefore, what this choice says tends to confirm that crime rates decreased because of decreases in the amount of lead in the water, and thus strengthens the support for the hypothesis.
Remember, when we have a cause-and-effect conclusion, if we can show that, when the cause is eliminated the effect is also, then we can strengthen the support for the conclusion.
