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 prepositional phrase is in the park. Camping is not part of the prepositional phrase.
The object of the prepositional phrase "during the Civil War" is the word "war" or since it is a proper noun, "Civil War."
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.