Preposition defines relationship of the words used in the sentence. Prepositional phrases are words that come alongside the prepositions. A determiner and adjective follows a preposition then by pronoun or noun. This is the object of the preposition. Overall, this makes up a phrase which can be an adjective, adverb, modifying noun, a locator in time or space or a teller of the when or where of events and happenings. In the sentence, Owen will need to take a nap _______ going to the concert The best answer would be b. Before.