Given $\mathrm{n}\left(\mathrm{U}\right)=20, \mathrm{n}\left(\mathrm{A}\right)=12, \mathrm{n}\left(\mathrm{B}\right)=9, \mathrm{n}\left(\mathrm{A}\cap \mathrm{B}\right)=4,$ where $\mathrm{U}$ is the universal set, A and B are subsets of U, then $\mathrm{n}\left({\left(\mathrm{A}\cup \mathrm{B}\right)}^{\mathrm{C}}\right)=$

• A

  17

• B

  9

• C

  11

• D

  3