The angle between the vectors $(\widehat{\mathrm{i}}+\widehat{\mathrm{j}}+\widehat{\mathrm{k}})$ and $(\widehat{\mathrm{i}}-\widehat{\mathrm{j}}-\widehat{\mathrm{k}})$ is

• A

  ${\sin }^{-1}\frac{\sqrt{8}}{3}$

• B

  ${\sin }^{-1}\left(\frac{1}{3}\right)+\frac{\mathrm{\pi }}{3}$

• C

  ${\cos }^{-1}\frac{\sqrt{8}}{3}$

• D

  ${\cos }^{-1}\sqrt{\frac{8}{3}}$