Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

Which of the following statements about credit ratings is most accurate?
Option A:Credit ratings can migrate over time.
Option B:Changes in bond credit ratings precede changes in bond prices.
Option C:Credit ratings are focused on expected loss rather than risk of default.

Answer: A