$A$ plane $\pi_1$ contains the vectors $\bar{i}+\bar{j}$ and $\bar{i}+2\bar{j}$. Another plane $\pi_2$ contains the vectors $2\bar{i}-\bar{j}$ and $3\bar{i}+2\bar{k}$. $\bar{a}$ is a vector parallel to the line of intersection of $\pi_1$ and $\pi_2$. If the angle $\theta$ between $\bar{a}$ and $\bar{i}-2\bar{j}+2\bar{k}$ is acute, then $\theta=$

  • A
    $\frac{\pi}{2}$
  • B
    $\frac{\pi}{4}$
  • C
    $\cos^{-1}\left(\frac{4}{3\sqrt{5}}\right)$
  • D
    $\cos^{-1}\left(\frac{2}{\sqrt{5}}\right)$

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