The question ask to choose among the following choices that best answer that could fit and support the statement in your question, and based on my further analysis about it, I came up with an answer of letter D. Substance. I hope you are satisfied with my answer and feel free to ask for more
"A. You know, of course, that she used to dive for her college swim team." does not have any errors in comma usage. "Of course" is almost always surrounded by commas.
Answer:
speaking is harder when in public because if you dont have the thing that you are going to say ready and if you are shy to speak in public.
