Use the octal system (base-$8$ numeral system) to calculate $\left (773\right )\_8 + \left (6\right )\_8$. The answer should be~\uline{~~~~~~~~~~}~. 
选项为:A:$\left (1001\right )\_8$  B:$\left (779\right )\_8$  C:$\left (111\right )\_8$  D:$\left (781\right )\_8$  请回答其中一个选项.