The trajectory of a projectile in a vertical plane is $y = \alpha x - \beta x^2$,where $\alpha$ and $\beta$ are constants and $x$ and $y$ are respectively the horizontal and vertical distances of the projectile from the point of projection. The angle of projection $\theta$ and the maximum height attained $H$ are respectively given by:

• A
  $\tan^{-1} \alpha, \frac{\alpha^2}{4\beta}$
• B
  $\tan^{-1} \beta, \frac{\alpha^2}{2\beta}$
• C
  $\tan^{-1} \alpha, \frac{4\alpha^2}{\beta}$
• D
  $\tan^{-1}(\frac{\beta}{\alpha}), \frac{\alpha^2}{\beta}$