Assuming that this is referring to the same paragraph that was posted before with this question, the best option would be "<span>b. He hides behind a tree" since this provides cover. </span>
<span>In F. Scott Fitzgerald's "The Great Gatsby," Gatsby calls Nick "old sport" as a term of endearment. The phrase also references Gatsby's manufactured affectations and his transition from poor James Gatz to rich Jay Gatsby. ... He calls not only Nick Carraway "old sport," but also Tom </span>
The subordinate clause in this sentence is 'Since I stopped vacuuming', and it is used as an adverb in this sentence, the adverb of time.
