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An unusual strategy called iron fertilization has recently been proposed to counteract the greenhouse effect, the process of global warming believed to be caused by a buildup of carbon dioxide in the atmosphere. It has been suggested that the Southern Ocean's unusually low concentrations of single-celled plants called phytoplankton result from an iron deficiency that keeps these organisms from making full use of the rich supplies of available nutrients. If so, fertilizing the waters with iron could enhance phytoplankton photosynthesis. Over time, enhanced photosynthesis would pull large amounts of carbon dioxide from the atmosphere, helping to counteract the buildup of this greenhouse gas.

The main purpose of the passage is to

Rationale

describe a recent suggestion for alleviating the problem of global warming.

The passage focuses on the concept of iron fertilization as a potential strategy to mitigate global warming by enhancing phytoplankton growth in the Southern Ocean. It discusses the link between iron deficiency and phytoplankton scarcity, suggesting that adding iron could increase photosynthesis and reduce atmospheric carbon dioxide levels.

A (compare various methods proven to be effective in helping to clean marine environments) YOUR ANSWER

This choice is incorrect because the passage does not provide a comparison of multiple methods for cleaning marine environments. It specifically discusses only the strategy of iron fertilization without reference to other methods or their effectiveness.

B (explain how single-celled marine organisms photosynthesize) YOUR ANSWER

While the passage mentions phytoplankton and their role in photosynthesis, it does not delve into the details of the photosynthesis process itself. The primary focus is on the suggestion of iron fertilization rather than a detailed explanation of the photosynthetic mechanisms.

C (describe a recent suggestion for alleviating the problem of global warming) CORRECT

This choice is correct as the passage centers around the proposal of using iron fertilization to enhance phytoplankton growth, which in turn could help reduce atmospheric carbon dioxide and combat global warming. This is the main theme conveyed throughout the text.

D (account for the relative scarcity of phytoplankton in the Southern Ocean) YOUR ANSWER

Although the passage does mention iron deficiency as a factor contributing to the low phytoplankton concentrations, it does not provide a thorough account of all reasons for their scarcity. Instead, the focus remains on the proposed solution of iron fertilization.

E (characterize the difference between the Southern Ocean and other large bodies of water) YOUR ANSWER

This choice is incorrect because the passage does not explore or compare the Southern Ocean with other large bodies of water in detail. It specifically addresses the challenges and suggestions related to phytoplankton in the Southern Ocean without broader comparisons.

Conclusion

The passage focuses on a novel approach to tackle global warming through iron fertilization to boost phytoplankton growth. By identifying the link between iron deficiency and phytoplankton scarcity, it highlights a potential method to enhance photosynthesis and reduce carbon dioxide levels, thereby addressing climate change. The other choices either misinterpret the passage's focus or stray from its primary purpose.

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