Concept:Use the correct articles: “an” for a single countable event, and “the” before the unique sun.Explanation:“Eclipse” is a singular countable noun, so it needs an article.“An” is used before a vowel sound, and this is the first mention of the eclipse.“The sun” is correct because there is only one sun.Therefore, the correct phrase is “an eclipse of the sun.”Answer:C. an eclipse of the sun