The correct option is A whom
The question concerns a person that the article is about. The question is in the passive voice, as the person is the object that receives an action by the subject. The "newspaper article" is the subject in the active voice (The newspaper article is about whom?) and the pronoun that would fill the blank is the object of the article. 'Whom' is a pronoun in the objective case, which refers to a noun that is at the receiving end of an action, hence option B is correct. 'Who' is a pronoun that refers to a subject in a sentence, for example, 'Who wrote this article?', 'who' is the subject that performs an action 'wrote'. It does not receive an action, hence option A is incorrect. 'Which' is mostly used to refer to things or a person from a group. When referring to a specific person or thing, 'which' is followed by the noun, example, 'which magazine do you write for?' Here it can't be used as 'which' is not followed by a noun, and it generally refers to things, hence option C is incorrect. 'That' is not an interrogative pronoun and if we say 'About that is the newspaper article?', the statement neither makes sense contextually nor grammatically.