问题如下：
Which of the following statements about credit ratings is most accurate?
选项：
A.Credit ratings can migrate over time.
B.Changes in bond credit ratings precede changes in bond prices.
C.Credit ratings are focused on expected loss rather than risk of default.
解释：
A is correct.
Credit migration is the risk that a bond issuer’s creditworthiness deteriorates, or migrates lower. Over time, credit ratings can migrate significantly from what they were at the time a bond was issued. An investor should not assume that an issuer’s credit rating will remain the same from the time of purchase through the entire holding period.
老师，可以解释一下C吗
