Whenever you're giving a presentation and want to engage your audience, you want to ensure you're giving a presentation that engages the audience. To do this, you want to foster discussion by asking open-ended questions that will spark a discussion amongst your audience. By asking open-ended questions, you will hopefully foster critical thinking that will in turn spark more discussion. People that are engaged in discussion generally learn more and retain more from the presentation itself.
Bearing this in mind, A and B can be marked off immediately as that is exactly what you want and are not the answer to your question. Answer C does not answer this question either because one and two word answers will not help confirm facts.
However, D is the right answer here. If you ask questions that only require one or two word answers, you won't have stimulating conversation and, thus, should be avoided at all costs.
