Difficulty: Medium

Average Score: 64%

Water that has large amounts of dissolved calcium and magnesium is referred to as hard water. Calcium and magnesium naturally occur in Earth materials such as limestone, magnesite, gypsum, and other minerals groundwater comes into contact with. Calcium is a vital component of bones and teeth. Calcium is also necessary for proper muscle action, blood clotting, and regulating the heartbeat. Magnesium is necessary for more than 300 biochemical processes in the body, such as regulating heartbeat and blood sugar levels, helping maintain normal blood pressure, and facilitating protein synthesis. The health benefits of drinking hard water have been well documented since the 1920s. One study investigated the effects of different amounts of dietary magnesium on rat survival rates. The first table shows the summary data from this study. Softening water has become a common practice in many homes. Soft water is water that has had the calcium and magnesium ions and other minerals removed to prevent the buildup of a residue called scale in pipes and appliances. Soft water also increases the effectiveness of soaps and detergents. Research around the health benefits of drinking hard water suggests that people may be at higher risk for certain diseases when their water lacks dissolved calcium and magnesium. The second table summarizes data from two human population studies that examined the role of dietary magnesium and cardiovascular health.

Which statement explains the central idea of the passage?

Diagram for question

Rationale

People may experience health benefits from drinking hard water because it contains magnesium.

The passage discusses the differences between salt water and freshwater ecosystems, but the central idea highlights the health benefits associated with drinking hard water, which is rich in minerals like magnesium. This focus on mineral content connects to the overall theme of the importance of water quality for health.

A (People should consume as much magnesium as possible to ensure good cardiovascular health.) YOUR ANSWER

While magnesium is indeed important for cardiovascular health, this statement does not directly relate to the central idea of the passage regarding the benefits of hard water. The passage emphasizes the health benefits derived from drinking water that contains magnesium rather than recommending a high magnesium intake in general.

C (People who live in rural environments are healthier than people who live in urban environments.) YOUR ANSWER

This statement introduces a comparison between rural and urban health that is not mentioned in the passage. The central idea focuses specifically on the benefits of hard water and its mineral content, without making any claims about geographic health disparities.

D (People should stop the practice of softening water because it removes minerals that are necessary for good health.) YOUR ANSWER

Although this statement touches on the topic of water softening and mineral removal, it does not encapsulate the passage's central idea. The focus of the passage is on the health benefits of hard water, while this statement suggests a course of action without directly addressing the advantages of mineral content in water.

Conclusion

The passage centers on the health benefits of hard water due to its magnesium content, making the correct answer B. The other options either stray from this focus, introduce unrelated concepts, or suggest actions that do not align with the central theme of the passage regarding the advantages of consuming hard water. Understanding this context is crucial for recognizing the significance of mineral-rich water in health discussions.

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