* Prepositions are words that show the relationship between a noun or pronoun and another word in the sentence. They often indicate location, time, direction, or manner.
Let's look at the words you provided:
* since: This word indicates a point in time and acts like a preposition. Example: "I've been waiting here since noon."
* except: This word indicates exclusion and acts like a preposition. Example: "Everyone went to the party except me."
* join: This word is a verb, meaning to connect or unite. It is not a preposition.
* past: This word can act as both an adjective and a preposition. As a preposition, it indicates movement beyond something. Example: "The car drove past the house."
Therefore, the word that is not a preposition is "join."