The correct option is A sharpened
The word 'blunt' refers to something not having a sharp edge or point.
Option A, pointed refers to having a sharpened or tapered tip at the end.
Option B, sharpened refers to filing the edge of something in order to make it sharper.
Option C, polished refers to becoming shiny as a result of being rubbed.
Option D, filed refers to making smooth or shape with a tool.
Thus, according to the meaning, the word 'sharpened' is the opposite of the word 'blunt'.