Changes to vegetation cover and other humanactivities influence carbon and nitrogen levels in soil,though how deep these effects extend is unclear.Hypothesizing that differences in land use lead todifferences in carbon and nitrogen levels that are notrestricted to the topsoil layer (0–30 cm deep),Chukwuebuka Okolo and colleagues sampled soilsacross multiple land-use types (e.g., grazing land,cropland, forest) within each of several Ethiopianlocations. They found, though, that across land-usetypes, carbon and nitrogen decreased to comparablylow levels beyond depths of 30 cm.Which choice best describes the overall structure ofthe text?A) It describes a phenomenon that scientists do notfully understand, explains a research team’shypothesis about that phenomenon, and thendescribes a finding that led the team to refine thehypothesis.B) It introduces an unresolved scientific question,presents a research team’s hypothesis pertainingto that question, and then describes anobservation made by the team that conflicts withthat hypothesis.C) It discusses a process that scientists aresomewhat unclear about, introduces competinghypotheses about that process, and then explainshow a research team concluded that one of thosehypotheses is likely correct.D) It explains a hypothesis that has been the subjectof scientific debate, discusses how a researchteam tested that hypothesis, and then presentsdata the team collected that validate thehypothesis.
Question
Changes to vegetation cover and other humanactivities influence carbon and nitrogen levels in soil,though how deep these effects extend is unclear.Hypothesizing that differences in land use lead todifferences in carbon and nitrogen levels that are notrestricted to the topsoil layer (0–30 cm deep),Chukwuebuka Okolo and colleagues sampled soilsacross multiple land-use types (e.g., grazing land,cropland, forest) within each of several Ethiopianlocations. They found, though, that across land-usetypes, carbon and nitrogen decreased to comparablylow levels beyond depths of 30 cm.Which choice best describes the overall structure ofthe text?A) It describes a phenomenon that scientists do notfully understand, explains a research team’shypothesis about that phenomenon, and thendescribes a finding that led the team to refine thehypothesis.B) It introduces an unresolved scientific question,presents a research team’s hypothesis pertainingto that question, and then describes anobservation made by the team that conflicts withthat hypothesis.C) It discusses a process that scientists aresomewhat unclear about, introduces competinghypotheses about that process, and then explainshow a research team concluded that one of thosehypotheses is likely correct.D) It explains a hypothesis that has been the subjectof scientific debate, discusses how a researchteam tested that hypothesis, and then presentsdata the team collected that validate thehypothesis.
Solution
The best choice that describes the overall structure of the text is B) It introduces an unresolved scientific question, presents a research team’s hypothesis pertaining to that question, and then describes an observation made by the team that conflicts with that hypothesis.
The text starts by introducing a scientific question that is not fully understood - how deep the effects of changes to vegetation cover and other human activities extend in influencing carbon and nitrogen levels in soil. It then presents a hypothesis by Chukwuebuka Okolo and colleagues that these differences in land use lead to differences in carbon and nitrogen levels that are not restricted to the topsoil layer. However, their findings showed that across land-use types, carbon and nitrogen decreased to comparably low levels beyond depths of 30 cm, which conflicts with their initial hypothesis.
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