* Prepositional phrases always start with a preposition. A preposition is a word that shows the relationship between a noun or pronoun (the object of the preposition) and another word in the sentence. Common prepositions include: on, in, at, to, from, by, with, etc.
* "Completed" is a verb, not a preposition. It describes an action.
Breakdown of the phrase:
* Completed: Past participle of the verb "to complete," acting as an adjective in this case.
* Her: Possessive pronoun, showing ownership of the assignment.
* Assignment: Noun, the object of the phrase.
This phrase is actually a participial phrase, which functions as an adjective modifying an implied noun. The full sentence could be something like:
* "She completed her assignment." In this sentence, the participial phrase "Completed her assignment" modifies the implied subject "she".