Answer:
The word which is the indefinite article is the following one:
an.
Explanation:
"An" is an indefinite article which is used when the word that follows it starts with a vowel sound, as it is the case of "honest", in which letter "h" is not pronounced. It is called an "indefinite" article because it does not define someone or something as being the only one who has a particular feature or is a particular thing. The opposite is the "definite" article.
Eg: John is an accountant. ("a" is the indefinite article, and it means John is one of many existing accountants)
John is the accountant here. ("the" is the definite article, since it defines John as being the only accountant at a certain place)
As for the other alternatives:
"it" functions as a subject pronoun in the sentence;
"her" functions as a possessive adjective in the sentence;
"that" functions as a connective in the sentence.
