If n is an integer then decimal digits must imply we are talking about numbers in the decimal system, I.e normal counting numbers as you know them.
Now pick any number n = 205 so S(n) = 2+0+5 = 9
Now S(n)-n = 205 - 9 = 196
196 is not divisble by 9, 10 or 11. Therefore we have found 1 example that contracdicts each of these sases therefore I think D is the answer.