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Weaken-CE. The correct answer choice is (E)
Since hard water contains more magnesium than soft water and people suffering from heart disease tend to have lower levels of magnesium in their blood, the author concludes that drinking soft water puts people at an increased risk of heart disease. Implicit in this conclusion is the assumption that the lower levels of magnesium are the cause, and not the effect, of heart disease:
- Cause Effect
Low levels of magnesium Heart disease
Answer choice (A): That magnesium deficiency is common plays no role in this argument, and certainly does not weaken the causality implicit in the author’s conclusion. This answer choice is incorrect.
Answer choice (B): If magnesium is needed to prevent sodium from increasing blood presure, low levels of magnesium might fail to avert the ill effects of sodium and therefore lead to the development of heart disease and high blood pressure. Since this answer choice strengthens the cause-and-effect relationship between low levels of magnesium and heart disease, it does the exact opposite of what is needed and is therefore incorrect.
Answer choice (C): This answer choice merely suggests another reason why magnesium intake might be disrupted. There is no evidence that the decreased ability to metabolize magnesium leads to decreased magnesium intake (for all we know, it might lead to a higher concentration of magnesium in the blood). Furthermore, there is no indication that the elderly are at a higher risk of developing heart disease and high blood pressure. This answer choice is incorrect.
Answer choice (D): Even if magnesium supplements inhibited the effectiveness of many medicines used to treat heart disease, this does not weaken the author’s conclusion that the low levels of magnesium can contribute to the development of heart disease too. It is perfectly possible that any level of magnesium intake that falls outside the normal range (too low or too high) can adversely affect cardiac health. This answer choice is incorrect.
Answer choice (E): This is the correct answer choice. See discussion above.