If the equation $4x^2+2\sqrt{3}xy+2y^2-1=0$ becomes $5x^2+Y^2=1$, when the axes are rotated through an angle $\theta$ , then $\theta$ is

• A

  ${15}^0$

• B

  ${30}^0$

• C

  ${45}^0$

• D

  ${60}^0$