Answer: D) Modest tone.
Step-by-step 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 excerpt from Part IV of Discourse on Method, we can see that Descartes uses a modest tone to explain his beliefs, we can see that in the way he describes himself as imperfect and lacking of qualities.