AB为什么不对

问题如下：

Which of the following provides call protection for CMBS investors at the structural level?

选项：

A.

Defeasance

B.

Prepayment lockout

C.

Sequential-pay tranches

解释：

The correct answer is C. Structural call protection is achieved through sequential-pay tranches in the CMBS as a lower-rated tranche cannot be paid down until the higher-rated tranche is completely retired.

A is incorrect because defeasance provides call protection at the individual loan level. Defeasance allows prepayment, but the borrower must purchase a portfolio of government securities that fully replicates the cash flows of the remaining scheduled principal and interest payments, including the balloon loan balance, on the loan.

B is incorrect because prepayment lockout provides call protection at the individual loan level. Prepayment lockout is a contractual agreement that prohibits any prepayments during a specified period.