Question

resident as earths living skin: biocrusts are thin layers of soil held together by surface - dwelling organisms that we bring to bear, and ecosystemic functions: fertilizing soil and aiding inceptions against erosion, ...... which choice completes the text so that it conforms to the conventions of standard english? question 1 (some label) options: (1) a recent study has estimated that these crusts reduce global dust emission by 60 percent each year. (2) these crusts reduces global dust emissions by an estimated 60 percent each year, according to a recent study. (3) an estimated 60 percent reduction in global dust emissions each year is due to these crusts, according to a recent study. (4) a recent study’s estimate is that these crusts reduce global dust emissions by 60 percent each year

Explanation:

To determine the correct option, we analyze subject - verb agreement and logical flow. The original context is about how dust storms (these crusts? Maybe a typo, likely “these crusts” or related to dust - reducing entities) affect dust emissions. Let's check each option:

• Option 1: “a recent study have estimated” has a subject - verb agreement error. “A study” is singular, so it should be “has” not “have”.
• Option 2: “Dust crusts reduces” has a subject - verb error. “Dust crusts” is plural, so the verb should be “reduce” not “reduces”.
• Option 3: “an estimated 60 percent reduction in global dust emissions each year is due to these crusts, according to a recent study.” This option has correct subject - verb agreement and logically connects the reduction in dust emissions to the crusts, with the source (recent study) properly cited.
• Option 4: “a recent study’s estimate is that these crusts reduce...” is wordy and less concise compared to Option 3, and the focus on the study's estimate is less direct in conveying the relationship between the crusts and dust emission reduction.

Answer:

C. an estimated 60 percent reduction in global dust emissions each year is due to these crusts, according to a recent study.