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 Rt△ABC, ∠BAC = 90.0, AD ⊥ BC at D, DE ⊥ AB at E, AD = 3.0, DE = 2.0, then the length of CD is ()
  Choices:
  (A) \frac{21}{2}
  (B) \frac{√{15}}{2}
  (C) \frac{9}{2}
  (D) \frac{3√{5}}{2}