They help the reader to follow your arguments by expressing the interactions involving diverse sentences or areas of a sentence. I think it should be “easy” or you may say “clean out” or “easy about”. “Smoothing” is undoubtedly much better than “smoothening”. But other dictionaries may possibly disagree. I http://cheap-seo-marketing-servi95161.ambien-blog.com/1613744/what-does-transition-words-sentences-mean