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24 Mar 2020, 02:24
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E
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Although water in deep aquifers does not contain disease-causing bacteria, when public water supplies are drawn from deep aquifers, chlorine is often added to the water as a disinfectant because contamination can occur as a result of flaws in pipes or storage tanks. Of 50 municipalities that all pumped water from the same deep aquifer 30 chlorinated their water and 20 did not. The water in all of the municipalities met the regional government’s standards for cleanliness, yet the water supplied by the 20 municipalities that did not chlorinated had less bacterial contamination than the water supplied by the municipalities that added chlorine.
Which one of the following, if true, most helps explain the difference in bacterial contamination in the two groups of municipalities?
(A) Chlorine is considered by some experts to be dangerous to human health, even in the small concentrations used in municipal water supplies.
(B) When municipalities decide not to chlorinate their water supplies, it is usually because their citizens have voiced objections to the taste and smell of chlorine.
(C) The municipalities that did not add chlorine to their water supplies also did not add any of the other available water disinfectants which are more expensive than chlorine.
(D) Other agents commonly added to public water supplies such as fluoride and sodium hydroxide were not used by any of the 50 municipalities.
(E) Municipalities that do not chlorinate their water supplies are subject to stricter regulation by the regional government in regard to pipes and water tanks than are municipalities that use chlorine.
24 Mar 2020, 05:31
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E is the best answer.
It is better to solve this question by eliminating the wrong answer choices.
Quote:
Although water in deep aquifers does not contain disease-causing bacteria, when public water supplies are drawn from deep aquifers, chlorine is often added to the water as a disinfectant because contamination can occur as a result of flaws in pipes or storage tanks. Of 50 municipalities that all pumped water from the same deep aquifer 30 chlorinated their water and 20 did not. The water in all of the municipalities met the regional government’s standards for cleanliness, yet the water supplied by the 20 municipalities that did not chlorinated had less bacterial contamination than the water supplied by the municipalities that added chlorine.
Which one of the following, if true, most helps explain the difference in bacterial contamination in the two groups of municipalities?
Which one of the following, if true, most helps explain the difference in bacterial contamination in the two groups of municipalities?
It is better to solve this question by eliminating the wrong answer choices.
Quote:
(A) Chlorine is considered by some experts to be dangerous to human health, even in the small concentrations used in municipal water supplies.
If this is true, then there is no need to use chlorine to purify the water for the 30 municipalities in whose water supply chlorine is added. A can be eliminated.Quote:
(B) When municipalities decide not to chlorinate their water supplies, it is usually because their citizens have voiced objections to the taste and smell of chlorine.
This does not help to explain the difference in bacterial contamination levels between the 30 municipalities that used chlorine and the 20 that doesn't use chlorine. If B is true, then we expect that the 20 municipalities that do not use chlorine to purify their water to have a higher level of bacterial impurities than the 30 that use chlorine as a purifying agent. B can be eliminated.Quote:
(C) The municipalities that did not add chlorine to their water supplies also did not add any of the other available water disinfectants which are more expensive than chlorine.
This leaves us with more questions than answers. Hence C does not help to explain the difference in the impurities levels in the 30 municipalities whose water supplies had more bacteria despite the use of chlorine to purify the water compared with those in the 20 municipalities that do not add chlorine. C can be eliminated.Quote:
(D) Other agents commonly added to public water supplies such as fluoride and sodium hydroxide were not used by any of the 50 municipalities.
Just as in C, D does not help to explain the difference in the levels of bacteria contamination in the 30 municipalities that use chlorine compared with those in the 20 municipalities that did not add chlorine to their water supplies. D can be eliminated.Quote:
(E) Municipalities that do not chlorinate their water supplies are subject to stricter regulation by the regional government in regard to pipes and water tanks than are municipalities that use chlorine.
Correct. This clearly explains the difference in the levels of bacteria contamination in the 30 municipalities that applied chlorine to their water compared to those in the 20 municipalities that did not apply chlorine to their water. We know from the information above that the added chlorine is to minimize the disease-causing bacteria that may be pipes and water storage tanks. So, it makes sense for the 20 municipalities who do not apply chlorine to record lower levels of bacteria contamination considering their pipes and storage tanks are subject to stricter regulation than the 30 municipilaties that apply chlorine to their water supply system. E is therefore the answer. 
24 Mar 2020, 07:23
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Quote:
Although water in deep aquifers does not contain disease-causing bacteria, when public water supplies are drawn from deep aquifers, chlorine is often added to the water as a disinfectant because contamination can occur as a result of flaws in pipes or storage tanks. Of 50 municipalities that all pumped water from the same deep aquifer 30 chlorinated their water and 20 did not. The water in all of the municipalities met the regional government’s standards for cleanliness, yet the water supplied by the 20 municipalities that did not chlorinated had less bacterial contamination than the water supplied by the municipalities that added chlorine.
Which one of the following, if true, most helps explain the difference in bacterial contamination in the two groups of municipalities?
(A) Chlorine is considered by some experts to be dangerous to human health, even in the small concentrations used in municipal water supplies.
(B) When municipalities decide not to chlorinate their water supplies, it is usually because their citizens have voiced objections to the taste and smell of chlorine.
(C) The municipalities that did not add chlorine to their water supplies also did not add any of the other available water disinfectants which are more expensive than chlorine.
(D) Other agents commonly added to public water supplies such as fluoride and sodium hydroxide were not used by any of the 50 municipalities.
(E) Municipalities that do not chlorinate their water supplies are subject to stricter regulation by the regional government in regard to pipes and water tanks than are municipalities that use chlorine.
Which one of the following, if true, most helps explain the difference in bacterial contamination in the two groups of municipalities?
(A) Chlorine is considered by some experts to be dangerous to human health, even in the small concentrations used in municipal water supplies.
(B) When municipalities decide not to chlorinate their water supplies, it is usually because their citizens have voiced objections to the taste and smell of chlorine.
(C) The municipalities that did not add chlorine to their water supplies also did not add any of the other available water disinfectants which are more expensive than chlorine.
(D) Other agents commonly added to public water supplies such as fluoride and sodium hydroxide were not used by any of the 50 municipalities.
(E) Municipalities that do not chlorinate their water supplies are subject to stricter regulation by the regional government in regard to pipes and water tanks than are municipalities that use chlorine.
ARGUMENT
[p] deep water does not contain disease bacteria;
[p] some water suppliers added chlorine and some did not;
[p] all passed contamination standards;
[p] those that did not had less bacterial contamination;
[as] so these had less bacteria in their pipes and/or tanks.
Ans (E) all passed standards, but those without chlorine (used to clean flaws in pipes and tanks) had stricter standards.
