Here's why:
* Adverb: When "before" modifies a verb, adjective, or another adverb, it's functioning as an adverb.
* Example: "He arrived before the deadline." ("before" modifies "arrived")
* Conjunction: When "before" connects two clauses, it's functioning as a conjunction.
* Example: "I'll call you before I leave." ("before" connects the clauses "I'll call you" and "I leave")
Prepositions connect a noun or pronoun to another word in the sentence and typically show the relationship of location, direction, or time. Common prepositions include "on," "in," "at," "to," "from," "by," "with," and "for."
Example:
* Preposition: "The book is on the table." ("on" connects "book" to "table")
* Adverb: "He arrived before the deadline." ("before" modifies "arrived")
* Conjunction: "I'll call you before I leave." ("before" connects the clauses)