Let $\theta$,$0 < \theta < \pi / 2$,be an angle such that the equation $x^2 + 4x \cos \theta + \cot \theta = 0$ has equal roots for $x$. Then $\theta$ in radians is

• A
  $\frac{\pi}{6}$ only
• B
  $\frac{\pi}{12}$ or $\frac{5 \pi}{12}$
• C
  $\frac{\pi}{6}$ or $\frac{5 \pi}{12}$
• D
  $\frac{\pi}{12}$ only