Explanation: The tone of a text or sentence is the author's or speaker's attitude towards the audience, the subject or even the characters of the text. There are many different kinds of tones, like: positive, negative, objective, sad, angry, etc. In the given sentence, the word that most clearly creates an inappropriate tone for a class presentation, is the corresponding to option B: Joke, because it isn't a word that should be used in an academic environment.
