question: Hint: Please answer the question and provide the correct option letter, e.g., A, B, C, D, at the end.
  Question: As shown in the figure, PA and PB are tangent to ⊙O to A and B respectively. Point C and point D are the moving points on line segments PA and PB, and CD always remains tangent to circle O. If PA = 8.0, then perimeter of △PCD is ()
  Choices:
  (A) 8
  (B) 12
  (C) 16
  (D) 不能确定