The correct option is D sharpened
Blunt means (of a cutting implement) not having a sharp edge or point. The opposite of blunt is sharpened, or make or become sharp or sharper. Hence, Option D is correct. Among the rest of the options, filed means smooth or shape with a file, polished means shiny as a result of being rubbed, pointed means having a sharpened or tapered tip or end. These options do not express the intended antonym, hence incorrect.