I was confused at first too. Basically it's preflipped and negated

He started with /N or /O -> /M and then immediately flipped it and negated it at the first step in the negating disjunction section. From there he did the "and" "or" swap to finish off the proper negation. The starting point isn't that first line, the first step has already been completed there. Hope this helps!

I'd venture to say that storytelling's consistent presence (being a universal aspect) doesn't necessarily render it something "important". It could just be a coincidental phenomena that doesn't imply any greater meaning or importance despite existing in past and present cultures. Who's to say how many other elements are universal aspects in cultures and how can we ascribe importance to it without any other support in the stimulus. Especially considering we're handling different time periods the general importance can wane (or increase) with time while its presence still exists. I think this option requires you to make a few more assumptions than option C, albeit I was also stuck between C and D.