DEFINE a noun as specific or unspecific.The definite article 'the' is USED with the name of things that are unique or already mentioned before.The article 'a' is used with the name of things that are not specific.The article 'an' is used with the words having the first letter as a vowel and having the sound of a vowel.If a word starts with a vowel but has the sound of a consonant, it will be preceded by the article 'a'.Example: a university, a union, a one rupee note, etc.In the GIVEN BLANK part of the sentence, the article 'the' will be used as a specific statement is being talked about in this question. Correct Sentence: He always speaks the truth. Any ABBREVIATION having the sound of a vowel will be preceded by the article 'an'.For example:He is a MLA.He is an MLA.