The correct option is
A an/a/no article
OPTION "A" is the correct answer.
EXPLANATION:
There are two types of articles:
DEFINITE ARTICLE (THE) : Article 'the' is used to refer to a DEFINITE thing or person.
INDEFINITE ARTICLE(A/AN): Article 'a/an' is used to refer to a thing or person in general. For instance: man, door etc.
Article 'a' is used with consonant sounds whereas article 'an' is used with vowel sounds.
In the first blank, article "an" will be used because article "a" is used when the speaker is making a general statement.
Similarly, In the second blank, article "a" will be used because article "an" is used when the speaker is making a general statement and the noun is having a consonant sound.
In the third blank, "no article" or "zero article" because 'no article' is used to refer to general ideas or general estimations.