There are approximately 80 to 100 prepositions in the English language. Prepositions are words that introduce information to the reader. This information can include where something takes place when or why something takes place. 
Prepositions don't stand alone. They work in groups of words that we call prepositional phrases. Aprepositional phrase begins with a preposition and ends in a noun. That noun is called the object of the preposition.
 Prepositions, in the form of prepositional phrases, provide specific information in a sentence for the reader. The reader would not know key and necessary facts about a sentence without a prepositional phrase. 
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I will not tell my answer byeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee.