Explanation
Correct answer: D.
Choice D is the best answer because it most logically completes the text’s discussion of internal carbon recycling by red coralline algae. In this context, “reuse” means using something again rather than disposing of it as waste. The text describes scientists’ surprise at “the extent of” internal carbon recycling by the algae, characterizing this finding as a departure from the more limited degree of activity that the scientists had expected to observe. The text goes on to explain that, in contrast to the scientists’ expectation that “some” carbon would be affected by the activity being described, the algae were found to “reabsorb nearly 40% of the carbon dioxide they produce during calcification processes and harness it for photosynthesis,” a specific example of their extensive capacity for taking in carbon and recycling, or reusing, it. Because the scientists thought the algae would use some of their own carbon dioxide again but were surprised by the extent of this activity, the context supports the idea that some reuse of carbon was expected.
Why the other choices are wrong
Choice A
Choice A is incorrect because it wouldn’t be logical in context to state that some “imitation,” or reproduction of something else, of carbon was expected. The text discusses the algae’s reabsorption and reuse of the carbon dioxide they produce, not any process by which carbon copies or reproduces something.
Choice B
Choice B is incorrect because stating that some “supply,” or available amount, of carbon was expected wouldn’t fit the contrast established within the text. The text contrasts the scientists’ expectations about carbon recycling in algae with their actual observations, noting that the scientists anticipated a more limited version of the recycling process they observed. This context doesn’t suggest that the scientists merely anticipated the presence of some amount of carbon.
Choice C
Choice C is incorrect because it wouldn’t be logical in context to state that some “examination,” or careful inspection, of carbon was expected. The text isn’t discussing scientists’ inspection of carbon, and carbon itself isn’t something that engages in inspection. Rather, the text focuses on the algae’s reabsorption and reuse of the carbon dioxide they produce.