I think advertisements used to play an essential role in society, but their position is less critical than before. For example, I was surprised that YouTube is trying to change its business model from advertisements to monthly billing. I believe the promotions are still beneficial, but it is becoming a classic method. I think that YouTube's trial stands as one piece of evidence. Instead of advertisements, I believe user-centered design has gained popularity nowadays. Of course, each of them has pros and cons. And I feel we should consider which to choose depending on the business purpose.

" I believe the promotions are still beneficial, but it is getting classical method. I think that YouTube's trial stands for one of the evidence." This bit is a little confusing and I'm not entirely sure what you're trying to say "And I feel we should consider choosing them depending on the business purpose." We don't start sentences with "And" or conjunctions for that matter (at least in formal situations - work, school, written reports, etc..). The sentence would have the same meaning and impact if you got rid of the the and. Overall, very good. You have a thorough understanding of the language.