Yes, since is a preposition (e.g. since noon).
It can also be a conjunction (since you arrived) or an adverb (gone ever since).
The prepositional phrase in "They haven't seen him since the party" is "since the party"
No.......... :'(
since the party
"In your backyard" is a prepositional phrase. The preposition is "in" and "backyard" is a noun, the object of the preposition.
which of these words is not a preposition past since join and except
for:)
The object of the prepositional phrase "during the Civil War" is the word "war" or since it is a proper noun, "Civil War."
The prepositional phrase is in the park. Camping is not part of the prepositional phrase.
In the wind is the prepositional phrase.
A prepositional phrase that modifies a noun or pronoun is an adjective prepositional phrase. An adjective prepositional phrase almost always follows the noun/pronoun it modifies.
Several has to be the subject since 'of the caves' is a prepositional phrase and 'are open' is the verb.
To is a preposition, but it's not a prepositional phrase unless there is an object of the preposition.