The answer is A: a clear central message.
The less information and clutter you have on your PowerPoint presentation, the more powerful your visual message will come out. Have a clear central message and use the 1-6-6 rule which states that, each PowerPoint slide should have 1 main idea, six bullet points, and a maximum of six words. Keep in mind that people came to hear you talk. Do not let slides limit you from slides that are chart junky or busy.