question: In \odot F, B, C, D, A are on the circle and A C is a diameter. \angle C F D is 4 a - 1 degrees. Find the measure of \angle A F B.
  Choices:
  A:72
  B:108
  C:120
  D:144
query_wo: Please directly answer the question and provide the correct option letter, e.g., A, B, C, D.
  Question: In \odot F, B, C, D, A are on the circle and A C is a diameter. \angle C F D is 4 a - 1 degrees. Find the measure of \angle A F B.
  Choices:
  A:72
  B:108
  C:120
  D:144
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: In \odot F, B, C, D, A are on the circle and A C is a diameter. \angle C F D is 4 a - 1 degrees. Find the measure of \angle A F B.
  Choices:
  A:72
  B:108
  C:120
  D:144
question_for_eval: In \odot F, B, C, D, A are on the circle and A C is a diameter. \angle C F D is 4 a - 1 degrees. Find the measure of \angle A F B.
  Choices:
  A:72
  B:108
  C:120
  D:144