Very simple, the prepositional phrase in the sentence is "Near the wooded island." The preposition is always at the beginning of the prepositional phrase and in this instance it would be 'near'. Likewise, the object of the preposition is always at the end of the prepositional phrase and in this case is 'island'. So the answer to this problem is C.
they should go because it may be of good to them
The answer would be D, since a quartet means 4, and a triumvirate means 3. So again the answer is 4:3.