The indefinite articles 'a' and 'an' are not used for nouns that are uncountable or cannot be counted. The noun here, 'salt' is an uncountable noun, so the options A and B are incorrect. The noun mentioned here is known by both the speaker as well as the listener, hence the article 'the' is used and is the correct answer. Option D is incorrect since the noun requires an article and it would be grammatically incorrect if not used.