Here's why:
* Prepositions show the relationship between a noun or pronoun and another word in the sentence. They typically indicate location, time, or direction. Examples: *in, on, at, to, from, by, with*.
* Adverbs modify verbs, adjectives, or other adverbs. They describe how, when, where, or to what extent something happens. Examples: *quickly, slowly, happily, nearly, almost, very*.
In your example:
* "Nearly" modifies the verb (e.g., "nearly finished," "nearly there") and tells us to what extent the action is happening.
Let me know if you have any other questions!