Which of the following best defines credulity as it is used in the passage below (paragraph 56)?

His father, smiling shamefacedly at his own credulity, held up the talisman, as his son, with a solemn face, somewhat marred by a wink at his mother, sat down at the piano and struck a few impressive chords.
Answer choices for the above question

A. extreme disbelief

B. firm faith in magic

C. absurd expectations

D. quickness to believe