Stating that something is, "simply the best" is bias because it is a personal preference. Not everybody will think this way, therefore it is A. A propaganda is giving information that comes from an unstable source or nature, making it biased to promote a certain idea. In the example, the person saying that Nike is the best would be giving off information that is not true for everyone's personal opinion, and makes Nike look better because it is promoting it.
Hope this helped, hmu if you have any questions :)
Yes, I'm not sure how to explain it but it needs to be there because there is a prepositional phrase (i think that is one) right there. But yes, it is necessary.
