In a presentation you want to use a language that your audience can easily understand. You want to make sure people feel welcome to the subject you're speaking about, so you have to use gentle language since they might not know as much as you do, and you want them to become interested.
Unassuming language will help you make sure concepts are clarified, that way if your audience don't know an specific concept, they still will understand the overall subject of the presentation with your explanation.
Therefore, correct answer is A.