Question

Which of these is a prepositional phrase?

Answer 1

D) under the window.
Under is the preposition in the phrase
Hope that helped!

Answer 2

The answer to your question would be that "under the window" is a prepositional phrase. That is, your answer would be D.

A prepositional phrase is a series of words made up of a preposition and its object. The object may be a noun, a pronoun, a gerund, or a clause.  Moreover, prepositional phrases function as adjectives or adverbs. In this case, the preposition "under" is the head of the prepositional phrase and it takes the NP "the window" as its object.