The correct answer is: D. no article
The word “dog” is a common noun, which means it refers to a general class of things. Common nouns are not usually preceded by articles.
The article “a” is used before singular common nouns that refer to something that is not specific or particular. For example, you might say “I saw a dog” if you saw a dog that you did not know or had not seen before.
The article “an” is used before singular common nouns that begin with a vowel sound. For example, you might say “I saw an elephant” because the word “elephant” begins with a vowel sound.
The article “the” is used before singular common nouns that refer to something that is specific or particular. For example, you might say “I saw the dog that bit me” if you were talking about a dog that you knew or had seen before.
In the sentence “There is . . . . . . . . dog,” the word “dog” is not preceded by any article. This is because the sentence is not referring to a specific or particular dog. It is simply stating that there is a dog somewhere.