A prepositional phrase is a phrase that has a preposition, and the object of the preposition (a noun, pronoun, gerund, or clause) and, it may have a modifier of the object (E.g. the). A subject is never part of a prepositional phrase, and this type of phrase can work as an adjective or an adverb.
As an adverb, the prepositional phrase answers the questions How? When? or Where. And as an adjective, it answers the question Which one?
10. The classes were all held <u>in the morning.</u>
<em>In: Preposition; the: modifier of the object; morning: object. </em>
<em>The prepositional phrase works as an adverb and it modifies the verb "held".</em>
11. Work began promptly <u>at nine o’clock. </u>
<em>At: Preposition; nine o'clock: object. The prepositional phrase works as an adverb and it modifies the verb "began" </em>
12. The students found the illustrations <u>of the problem</u> interesting and helpful.
<em>Of: Preposition; the: modifier of the object; problem: object. The prepositional phrase works as an adjective and it modifies the noun "the illustrations" </em>
13. Teachers located materials <u>on different topics. </u>
<em>On: Preposition; different topics: object. The prepositional phrase works as an adverb and it modifies the verb "located" </em>
14. Classes<u> like these</u> kept the students busy.
<em>Like: Preposition; these: object. The prepositional phrase works as an adjective and it modifies the noun "Classes".</em>