question: As shown in the figure, the straight line AB is tangent to circle O at point A, the radius of circle O is 1.0, if angle OBA = 30.0, then the length of OB is ()
  Choices:
  A:1
  B:2
  C:√{3}
  D:2√{3}
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 straight line AB is tangent to circle O at point A, the radius of circle O is 1.0, if angle OBA = 30.0, then the length of OB is ()
  Choices:
  A:1
  B:2
  C:√{3}
  D:2√{3}
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 straight line AB is tangent to circle O at point A, the radius of circle O is 1.0, if angle OBA = 30.0, then the length of OB is ()
  Choices:
  A:1
  B:2
  C:√{3}
  D:2√{3}
question_for_eval: As shown in the figure, the straight line AB is tangent to circle O at point A, the radius of circle O is 1.0, if angle OBA = 30.0, then the length of OB is ()
  Choices:
  A:1
  B:2
  C:√{3}
  D:2√{3}