The correct answer is D. no article.
The article "a" is used before singular nouns that refer to a general or unspecified thing. The article "an" is used before singular nouns that begin with a vowel sound. The article "the" is used before singular nouns that refer to a specific or particular thing.
In the sentence "There is no life on Mars," the word "Mars" is a proper noun, which is a noun that refers to a specific person, place, or thing. Proper nouns are always capitalized and do not take an article.
The other options are incorrect because they are all articles.
