The source says "common", not "most common". When I go to the source that the source cites (COCA) and type in what is apparently the code for adverb ("[rr]"), I don't get exactly the same list as is presented here.
Yes, I've viewed other sources too, and it's the same list, so I gave a link to the one that is easiest to read. Besides, that source is reliable, taken from Brigham Young University.