已知全集$U=\left\{1,2,3,4\right\}$,集合$A=\left\{1,2\right\},B=\left\{2,3\right\}$,则${\complement }_U(A\cup B)=$

$\left\{1,3,4\right\}$

$\left\{3,4\right\}$

$\left\{3\right\}$

$\left\{4\right\}$