Question

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

Answer 1

Under the desk

Explanation:

Prepositions and prepositional phrases give us more information about the object in question.

In the above question, the sentence reads:

"Alan dropped the paper under the desk".

The preposition is "under" and the propositional phrase is "under the desk". One way to tell is we can break the sentence down into a little conversation and get the same information through a series of questions:

Person 1 - Alan dropped the paper.
Person 2 - Where did it go?
Person 1 - Under the desk.

Answer 2

"under the desk" is the prepositional phrase in this sentence

Explanation:

It tells where the paper was dropped.

A simple prepositional phrase will have:
a preposition + an article + a noun or pronoun.

It can also contain information modifying (telling more about) the noun or pronoun, for example:

"Alan dropped the paper under Robert's desk."
or
"Alan dropped the paper under the desk in the corner of the front row."

There are lots of prepositions, and not all of them consist of only one word, for example:
in the desk
on the desk
at the desk
behind the desk
in front of the desk
because of the desk
in order to fix the desk
to mention just a few.

You may want to check out this web site:
https://www.englishclub.com/grammar/prepositions-list.htm
for a longer list.

From there, there's a link to:
https://www.englishclub.com/vocabulary/prepositions/list.htm
with more, including multiple-word prepositions.