Answer:
C. After a delicious lunch.
Step-by-step explanation:
Prepositional phrase are those groups of words that cannot make a complete sentence on their own. It is most commonly identified by the structure of the phrase, starting with a preposition and usually ending with a noun.
In the sentence "After a delicious lunch, they discussed where they wanted to go next", the prepositional phrase is "After a delicious lunch".
In this sentence, the word "after" is a preposition and "lunch" is the noun, while "delicious" modifies the object "lunch".