Use summation notation to rewrite the given sum in terms of $k.$

$\frac{8}{9*10}\frac{9}{10*11}$ cdots $\frac{n}{(n1)(n2)}$

Select the correct expression.

${\displaystyle \underset{k=1}{\overset{}{}}}\frac{k}{(k1)(k2)}$

${\displaystyle \underset{k=8}{\overset{}{}}}\frac{k}{(k1)(k2)}$

${\displaystyle \underset{k=8}{\overset{k}{}}}\frac{n}{(n1)(n2)}$

${\displaystyle \underset{k=8}{\overset{n}{}}}\frac{k}{(k1)(k2)}$

${\displaystyle \underset{k=8}{\overset{n}{}}}\frac{n}{(n1)(n2)}$