What is the prepositional phrase in sentence Alan dropped paper under desk?

The prepositional phrase in the sentence "Alan dropped paper under the desk" is "under the desk".

Here's why:

* Prepositional phrases start with a preposition (like "under") and end with a noun or pronoun (like "desk").

* Prepositions show the relationship between the noun or pronoun and the rest of the sentence. In this case, "under" tells us where the paper was dropped.