问题如下图：
选项：
A. 
B. 
C. 
解释：
NO.PZ2017012501000014 问题如下 Whiof the following investments is least subjeto prepayment risk? A.Auto loreceivable–backesecurities B.Commercimortgage-backesecurities (CMBSs) C.Non-agenresintimortgage-backesecurities (RMBSs) B is correct.A criticfeature thfferentiates CMBSs from RMBSs is the call protection provito investors. investor in a RMis exposeto consirable prepayment risk because the borrower hthe right to prepthe lobefore maturity. CMBSs provi investors with consirable call protection thcomes either the structure level or the lolevel.考点prepayment risk解析A车贷，C房贷都属于amortizing loan，即本金摊销在中间各期，以月供的形式进行归还的。这样就会有本金的偿付，会面临prepayment risk。CMBS为投资者提供了call protection，避免投资者受到提前还款带来的风险。题目要我们选择最不会遭受prepayment risk的投资方式，所以选择CMBS。故B正确。 non-agenRMBS不是只考虑cret risk吗？为什么不选？
照这样说的话 RMBS也可以通过分层来降低prepayment risk啊？ 那为什么不能选C
A为什么不能选
想问一下，CMBS为什么一定包含call protection？
