Nhận biết (M1)

Despite potential independent confirmation, the apparent detection in 2020 of phosphine (PH₃)—a gas that on Earth almost exclusively derives from biological sources—in Venus's cloud deck remains controversial, in part because Venus is thought to be uninhabitable. To evaluate such a finding's plausibility, William Bains et al. modeled multiple abiotic PH₃ pathways, including geochemical, atmospheric, and photochemical reactions, but none adequately explain the observed levels of PH₃. If Venusian PH₃ does exist, it would indicate insufficiencies in the current consensus on Venus's chemistry.

Which choice best describes the overall structure of the text?

• A.

  It introduces an unexpected observation of a particular gas in Venus's atmosphere, presents an effort to investigate possible mechanisms that could explain that observation, and then notes an implication of that investigation's findings.

• B.

  It explains why the consensus view of a particular gas in Venus's atmosphere has recently become controversial, expands on a scientific team's reasons for questioning that consensus, and then suggests that future observations of Venus's atmosphere will likely be needed to settle the controversy.

• C.

  It compares the levels of a particular gas on Venus and Earth, sketches the chemical processes that account for differences in these levels, and then addresses some of the practical challenges of studying the presence of this gas on Venus more closely.

• D.

  It outlines recent efforts to confirm the presence of a particular gas in Venus's atmosphere, summarizes a research team's evaluations of those efforts' methodological shortcomings, and then explains why that team remains skeptical of the gas's future detection.