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, points A, B, and C are three points on ⊙O, and the straight line CD and ⊙O are tangent to point C. If ∠DCB = 40.0, then the degree of ∠CAB is ()
  Choices:
  (A) 40°
  (B) 50°
  (C) 80°
  (D) 100°