Question

A prepositional phrase that modifies a noun is acting as a(n)

a.verb.
b.adverb.
c.clause.
d.adjective.

Answer 1

noun is a person place or thing ( or idea ) and something that modifies a noun is an adjective. so the answer would be: D. adjective    hope this helps :) 

Answer 2

d.adjective.

Step-by-step explanation:

A prepositional phrase that modies a noun is functioning as an adjective. For example: The woman in red is my sister. In red refers to a woman in particular ; the speaker wants to make it clear to which woman he is referring to. In this other example : The man by the window is my boss, the prepositional phrase by the window is telling , again, to which man the speaker is refering.