已知 $U=\left\{1,2,3,4,5,6,7,8\right\},A=\left\{1,3,5,7\right\},B=\left\{2,4,5\right\}$,则 ${\complement }_U\left(A\cup B\right)$=

{6,8}

{5,7}

{4,6,7}

{1,3,5,6,8}