Descartes' ontological (or a priori) argument is both one of the most fascinating and poorly understood aspects of his philosophy. Fascination with the argument stems from the effort to prove God's existence from simple but powerful premises. Existence is derived immediately from the clear and distinct idea of a supremely perfect being. Ironically, the simplicity of the argument has also produced several misreadings, exacerbated in part by Descartes' tendency to formulate it in different ways.
D) Modest tone.
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.