问题如下图：记得很清楚，刚做过一道题，说call protection可以increase credit rating，我还觉得很奇怪，那到底call protection可不可以increase credit rating呢？谢谢！
选项：
A. 
B. 
C. 
解释：
NO.PZ2017012501000012 请问bt-to-servicoverage是什么？为什么会影响信用评级？在课件哪里呀？
Call protection Balloon payments A is correct. If specific ratios of to servicoverage are nee anthose ratios cannot met the lolevel, subornation is useto achieve the sirecret rating. Call protection protects investors against prepayment risk. Balloon payments increase the risk of the unrlying loans. a内部信用增级不是只是各个分层不一样但是总体并没有改变吗？
NO.PZ2018062012000012 的答案说call protection可以increase cret rating，是不是有矛盾？到底哪道题答案是对的，该如何理解？谢谢。
感觉知识点陌生，视频课哪里有讲解？
