下列运算正确的是 $\mathit{(}$　　 $\mathit{)}$

A． ${\mathit{a}}^{\mathit{3}}\mathit{·}{\mathit{a}}^{\mathit{3}}\mathit{=}\mathit{2}{\mathit{a}}^{\mathit{6}}$B． ${\mathit{a}}^{\mathit{3}}\mathit{+}{\mathit{a}}^{\mathit{3}}\mathit{=}\mathit{2}{\mathit{a}}^{\mathit{6}}$C． ${\mathit{\left(}{\mathit{a}}^{\mathit{3}}\mathit{\right)}}^{\mathit{2}}\mathit{=}{\mathit{a}}^{\mathit{6}}$D． ${\mathit{a}}^{\mathit{6}}\mathit{·}{\mathit{a}}^{\mathit{2}}\mathit{=}{\mathit{a}}^{\mathit{3}}$