Answer: Photograph
Explanation: Of the answer choices listed, "Photograph" is the most correct answer. A photograph provides a representation of an event that is unable to express impartiality through any means other than that of post-production editing; which requires specific resources and the skills to utilize them accordingly. Unlike the other answer choices, this medium of expression is initially objective and impartial; the others are influenced by human subjectivity both initially and finally. A speech given to represent an event is subject to bias and subjectivity, both of which deviate from objectivity and impartiality, by the writer and speaker of the speech. A cartoon drawn to represent an event relies on the skill level of the artist to depict the event accurately, and is also subject to bias by the artist. An editorial written to represent an event is subject to bias and subjectivity by the author.