Known $$A=\frac{{{3}^{2019}}+1}{{{3}^{2020}}+1}$$，$$B=\frac{{{3}^{2020}}+1}{{{3}^{2021}}+1}$$, compare between $$A$$ and $$B$$． 
选项为:A:$A=B$  B:$A\textgreater B$  C:$A\textless B$  D:All of the above  E:None of the above  请回答其中一个选项.