Answer: They are learning a new vocabulary. C
Explanation:
Prepositional phrases express position and relation in space and time and begin with a preposition. The only prepositional phrases here are 1) "in the house," 2) "through the tunnel," and 3) "in 45 minutes." So, whichever of these are underlined in the problem, the corresponding sentences are the answers. Hope that helps!
Based of the research I just made about the CLEP exam, D. seems like the appropriate answer.
