ANSWER:
The correct answer is under the desk.
Alan dropped the paper under the desk.
STEP-BY-STEP EXPLANATION:
A prepositional phrase is a group of words consisting of a preposition, its object, and any words that modify the object. Most of the time, a prepositional phrase modifies a verb or a noun. These two kinds of prepositional phrases are called adverbial phrases and adjectival phrases, respectively.
At a minimum, a prepositional phrase consists of one preposition and the object it governs. The object can be a noun, a gerund (a verb form ending in “-ing” that acts as a noun), or a clause.
