The angle between the diagonal of a quadrilateral formed by the lines $\frac{\mathrm{x}}{\mathrm{a}}+\frac{\mathrm{y}}{\mathrm{b}}=1,\frac{\mathrm{x}}{\mathrm{b}}+\frac{\mathrm{y}}{\mathrm{a}}=1,\frac{\mathrm{x}}{\mathrm{a}}+\frac{\mathrm{y}}{\mathrm{b}}=2$ and $\frac{\mathrm{x}}{\mathrm{a}}+\frac{\mathrm{y}}{\mathrm{a}}=2$ is 

• A

  $\frac{\mathrm{\pi }}{4}$

• B

  $\frac{\mathrm{\pi }}{2}$

• C

  $\frac{\mathrm{\pi }}{3}$

• D

  $\frac{\mathrm{\pi }}{6}$