Constellations, groups of stars, provide astronomers with a roadmap of the galaxy.
Answer:
groups of stars
Explanation:
Groups of stars is a nonrestrictive <u>appositive phrase</u> that provides additional information about the noun <em>Constellations</em>. It is set off with commas because the information it provides is not necessary for identifying the noun it describes.
The correct answer is C.
In A, the correct word should be "affected."
In B, the correct word should be "effect."
In D, the correct word should be "complemented."
Only C. uses the word in quotations correctly: The teacher referenced the book.