Let $\bar{a} = \bar{i} + 2\bar{j} + 2\bar{k}$ and $\bar{b} = 2\bar{i} - \bar{j} + p\bar{k}$ be two vectors. If the angle between $\bar{a}$ and $\bar{b}$ is $60^{\circ}$, then $p =$

  • A
    $\frac{\sqrt{7}}{3\sqrt{2}}$
  • B
    $\frac{3\sqrt{5}}{\sqrt{7}}$
  • C
    $\frac{\sqrt{3}}{\sqrt{7}}$
  • D
    $\frac{\sqrt{5}}{\sqrt{7}}$

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