问题如下图：
选项：
A. 
B. 
C. 
解释：
老师，这道题的意思是让求信用评级的改变么？求出来是0.23437%呀。。谢谢
NO.PZ201812310200000201 问题如下 The most appropriate response to Kowalski’s question regarng cret rating migration is thit has: A.a negative impact. B.no impact. C.a positive impact. A is correct. Cret spremigration typically reces the expectereturn for two reasons. First, the probabilities for rating changes are not symmetrically stributearounthe current rating; they are skewetowara wngra rather thupgra. Secon the increase in the cret spreis mularger for wngras this the crease in the sprefor upgras. 有negative impace是否是因为成为BB的概率为6.95%，成为A的概率为4.8%下调的概率大于上升的概率，所以是negative impact。或者说我这个分析跟题目没啥关系？
NO.PZ201812310200000201 老师好， 我没太明白这道题在考什么，答案解析我也没太看明白，麻烦老师帮忙讲讲，谢谢
请问这个结论在讲义哪里提到过？
