It's given that the noun 'decision' is specific and has been mentioned before. The definite article 'the' is used for specific nouns like 'decision' in the given sentence, hence option C is correct. Indefinite articles 'a' and 'an' are used to modify nouns that are non-specific and have not been mentioned before since the 'decision' is a specific noun, options A and B are incorrect. An article is not used before nouns when we refer to them in general, 'decision' being a specific noun makes the option D incorrect.