The correct answer is D. no article.
The word “politician” is a common noun, which means that it refers to a general class of people. Common nouns are not typically preceded by articles.
In this case, the speaker is not referring to a specific politician, but rather to politicians in general. Therefore, the article “a” or “an” would not be appropriate. The article “the” would also be incorrect, as it would imply that the speaker is referring to a specific politician.
Without an article, the sentence reads more smoothly and naturally. It also allows the reader to interpret the sentence in a more general way.