Final answer:
The best revision for the phrase "snow covered" when used as a compound modifier before a noun is option (d) Snow-covered, which is hyphenated according to English grammar rules.
Step-by-step explanation:
The question requires the selection of the best revision for the phrase "snow covered." The correct revision should adhere to standard English rules for compound modifiers. When used as an adjective before a noun, the phrase should be hyphenated. Therefore, the best revision is option (d) Snow-covered.
For instance, when describing a meadow, the correct sentence would be: "The snow-covered meadow was a breathtaking sight." This indicates the meadow is covered in snow, and the hyphen is used because "snow-covered" is a compound modifier that is describing the noun "meadow."