Tổng

Câu hỏi: Tổng $$\begin{gathered} S=\frac{1}{2017}(2.3C_{2017}^2+3.3^2{C}_{2017}^3 \\ +4.3^3{C}_{2017}^4+...+k.3^{k-1}{C}_{2017}^k \\ +...+2017.3^{2016}{C}_{2017}^{2017}) \end{gathered}$$bằng

A. $4^{2016}-1$

B. $3^{2016}-1$

C. $3^{2016}$

D. $4^{2016}$