Robert Frost's poem has the structure of a lyric poem. If you think about it, this poem could be put to some music and be sung, just like song lyrics.
Based on the context of the paragraph, I would say A. Before.
A prepositional phrase consists of the preposition and its complement. From the given sentences above, the sentence in which the prepositional phrase best modifies the verb saw is option C. Through the window, I saw the bird flying. The prepositional phrase in this sentence is "through the window".
