question: As shown in the figure, the right triangle ABC and the equilateral triangle ABD are respectively drawn with the line segment AB as the edge, where angle ACB = 90.0. Connect CD, when the length of CD is the largest, the size of angle CAB is ()
  Choices:
  A:75°
  B:45°
  C:30°
  D:15°
query_wo: Please directly answer the question and provide the correct option letter, e.g., A, B, C, D.
  Question: As shown in the figure, the right triangle ABC and the equilateral triangle ABD are respectively drawn with the line segment AB as the edge, where angle ACB = 90.0. Connect CD, when the length of CD is the largest, the size of angle CAB is ()
  Choices:
  A:75°
  B:45°
  C:30°
  D:15°
query_cot: Please first conduct reasoning, and then answer the question and provide the correct option letter, e.g., A, B, C, D, at the end.
  Question: As shown in the figure, the right triangle ABC and the equilateral triangle ABD are respectively drawn with the line segment AB as the edge, where angle ACB = 90.0. Connect CD, when the length of CD is the largest, the size of angle CAB is ()
  Choices:
  A:75°
  B:45°
  C:30°
  D:15°
question_for_eval: As shown in the figure, the right triangle ABC and the equilateral triangle ABD are respectively drawn with the line segment AB as the edge, where angle ACB = 90.0. Connect CD, when the length of CD is the largest, the size of angle CAB is ()
  Choices:
  A:75°
  B:45°
  C:30°
  D:15°