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Difficulty: EasyCentral Ideas

Beavers are known for building dams that alter their local environments. By blocking streams, these dams slow the flow of water and create large ponds and wetlands. These newly formed wetlands serve as critical habitats for a wide variety of plants, insects, and fish. Additionally, the slowed water allows sediment to settle, which helps filter out pollutants and improves downstream water quality. Ultimately, the construction of beaver dams plays a vital role in enhancing biodiversity and maintaining healthy freshwater ecosystems.

Which choice best states the main idea of the text?

  1. A
    Animal species play a crucial role in shaping the physical landscapes and chemical compositions of the Earth's ecosystems.
  2. B
    Beavers construct dams primarily to filter sediment and remove harmful pollutants from downstream water sources.
  3. The dams built by beavers create wetland habitats that support diverse species and improve the health of freshwater ecosystems.Answer
  4. D
    Without the presence of beaver dams, freshwater ecosystems would eventually collapse and lose all of their biodiversity.

Answer

The correct answer is the option stating that beaver dams create wetland habitats that support diverse species and improve the health of freshwater ecosystems.
The correct answer accurately summarizes the text's description of beaver dams and their ecological impact. The passage explains that the dams slow water flow to create wetlands, which provides habitat for diverse species and filters pollutants, thereby concluding that the dams are vital for enhancing biodiversity and maintaining healthy freshwater ecosystems.

Step-by-Step Solution

1
Read the passage to identify the primary subject and the main point the author is making about that subject.
The passage describes how beavers build dams, which creates ponds and wetlands, benefits various species (plants, insects, fish), and filters pollutants, concluding that this plays a vital role in freshwater ecosystems.
Understanding the general scope and structure of the passage helps isolate the central idea from supporting details.
2
Evaluate the answer options to find the one that summarizes the overall message without being too broad or too specific.
The option stating that beaver dams create wetland habitats that support diverse species and improve the health of freshwater ecosystems captures the entire passage's scope.
The correct main idea must be supported by the passage as a whole, rather than focusing on a single detail or making extreme, unsupported claims.

Key Concept

Identifying the main or central idea of an academic or scientific passage.
Estimated Time:45s
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