What is the acute angle between the planes $x+y+2 z=3$ and $-2 x+y-z=11$ ?

• A

  $\pi / 5$
• B

  $\pi / 4$
• C

  $\pi / 6$
• Correct answer
  D

  $\pi / 3$

Hence, the correct answer is option: 'D'.