Marine biologists once theorized that the sudden proliferation of deep-sea glass sponge reefs off the Pacific coast was primarily driven by recent changes in ocean water temperature. However, this hypothesis overlooks crucial historical sedimentation data. High-resolution oceanographic core samples demonstrate that these sponge colonies have maintained stable growth cycles for over three millennia, regardless of thermal fluctuations. Because glass sponge structures rely on dissolved silica rather than temperature stability to construct their structural frameworks, the recent expansion is actually attributable to agricultural runoff that boosted coastal silica concentrations.
Which of the following statements accurately describe the structural function of the boldfaced portions in the argument above? Select all that apply.
- The first boldfaced portion presents a hypothesis that the argument seeks to refute.Answer
- The second boldfaced portion states the main conclusion that the overall argument advocates.Answer
- CThe first boldfaced portion provides factual evidence that directly supports the author's main conclusion.
- DThe second boldfaced portion is a intermediate premise used to show that glass sponges are indifferent to ocean silica levels.
- EThe first boldfaced portion is an unstated assumption required for the silica runoff explanation to hold true.