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, in the diamond ABCD, ∠BAD = 120.0, the length of the diagonal AC is 3.0, then the perimeter of the diamond ABCD is ()
  Choices:
  (A) 3
  (B) 6
  (C) 9
  (D) 12