问题如下：
Which of the following statements is incorrect regarding ratings on sovereigns and corporations？
选项：
A.When the market environment changes, rating agencies can not change their ratings in time.
B.Ratings agencies have been accused of being far too pessimistic in their assessments of both corporate and sovereign ratings.
C.When one rating agency lowers or raises a sovereign rating, other rating agencies seem to follow suit.
D.When a rating agency changes the rating for a sovereign multiple times in a short time period, it is admitting to failure in its initial rating assessment.
解释：
B is correct
考点：The Biases Affecting A Rating System.
解析：
评级机构对公司和主权评级的评估过于乐观而不是悲观，B说法错误。
评级机构在评级的时候也有羊群效应，即如果一家机构改变了对某个公司或者政府的评级，其它机构也会效仿，而且评级往往对于市场变化的反应比较滞后。另外如果评级机构短时间内频繁调整对一个主权政府的评级，说明它初始的评级是失败的。A、C、D均是正确的选项。
这道题答对了，但是还想具体问问d选项应该怎么理解，谢谢
