问题如下图：
选项：
A. 
B. 
C. 
D. 
解释：
请问什么叫excess spread 给senior tranches 提供直接保护？spread 不是equtiy 层次最高嘛？
另外，timing of losses 为什么会impact excess spreads？ 谢谢
NO.PZ2016082405000100 Whiof the following subprime characteristiprovi reprotection for senior tranches? Subornation, excess sprea anshifting interest. Subornation, prepayments, anshifting interest. Overcollateralization, excess sprea antiming of losses. Overcollateralization, excess sprea anprepayments. A Subornation, excess sprea anshifting interest provi protection for senior tranches. Overcollateralization also provis protection for senior tranches. Timing of losses impacts excess sprea. Prepayments caccelerate or celerate the cash flows to senior tranches. 看到老师回复说shifting interest前期某段时间（一般是36个月），其他层只还利息，只有senior层还的事本金+利息。 问题那么senior直接前期就还了本金，这不是和prepayment一样吗？对s层应该是不好的事情吧？
NO.PZ2016082405000100 Whiof the following subprime characteristiprovi reprotection for senior tranches? Subornation, excess sprea anshifting interest. Subornation, prepayments, anshifting interest. Overcollateralization, excess sprea antiming of losses. Overcollateralization, excess sprea anprepayments. A Subornation, excess sprea anshifting interest provi protection for senior tranches. Overcollateralization also provis protection for senior tranches. Timing of losses impacts excess sprea. Prepayments caccelerate or celerate the cash flows to senior tranches. 1.Timing of losses impacts excess sprea他是如何impacts excess sprea呢 2.其实overcollateralization是直接影响的吧？只不过他里面包括了其他错误的所以不选对吗？
Whiof the following subprime characteristiprovi reprotection for senior tranches? Subornation, excess sprea anshifting interest. Subornation, prepayments, anshifting interest. Overcollateralization, excess sprea antiming of losses. Overcollateralization, excess sprea anprepayments. A Subornation, excess sprea anshifting interest provi protection for senior tranches. Overcollateralization also provis protection for senior tranches. Timing of losses impacts excess sprea. Prepayments caccelerate or celerate the cash flows to senior tranches. shifting interest 指的是啥？
overcollateralization的是equity tranche吧？所以算是间接保护了senior？
C错在哪里？下面说overcollateralization also provi protection for seniir tranches
