I can't tell what's the poem and what's the question, maybe can you put the poem in quotations? Either that or you didn't write it correctly.
The answer is B, movie. "Action" is used as an adjective here, so it cannot be an object when there is no noun present. "Saw" is a verb. "I" is the subject, so the only remaining option is B, movie. The question to easily determine what the object is would be "What did you see?" And the answer would be "A movie".
The prepositional phrase is "on a high shelf" since ON is a preposition.