The correct answer is: a
The word “owl” is a common noun, which means it refers to a general class of things. In this case, the speaker is referring to an owl in general, not a specific owl. Therefore, the indefinite article “a” is used.
The definite article “the” is used to refer to a specific thing or person. For example, if the speaker had said “Yesterday I saw the owl that lives in the tree outside my window,” then the definite article “the” would be correct.
The article “an” is used before singular nouns that begin with a vowel sound. For example, if the speaker had said “Yesterday I saw an eagle flying overhead,” then the article “an” would be correct.
The answer “none of the above” is incorrect because the speaker is clearly referring to an owl.