Two plane mirrors are kept on a horizontal table making an angle $\theta$ with each other as shown schematically in the figure. The angle $\theta$ is such that any ray of light reflected after striking both the mirrors return parallel to its incident path. For this to happen, the value of $\theta$ should be

• A

  $30°$
• B

  $45°$
• C

  $60°$
• Correct answer
  D

  $90°$

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