Mortgage的每月现金流并不是Constant的呀

问题如下：

What is the difference between the pattern of cash flows provided by a fixed rate mortgage and the pattern of cash flows provided by a U.S. Treasury bond? Assume no prepayments and no defaults on the mortgage.

选项：

A.

A fixed-rate mortgage provides semi-annual cash flows that include both interest and principal, while a bond provides monthly coupons and a final payment of principal.

B.

A fixed-rate mortgage provides monthly cash flows that decrease over time, while a bond provides semi-annual coupons that increase over time.

C.

A fixed-rate mortgage provides monthly cash flows that are constant for the whole life of the mortgage, while a bond provides semi-annual coupons and a final payment of principal.

D.

A fixed-rate mortgage provides annual cash flows that are constant for the whole life of the mortgage, while a bond provides monthly coupons and a final payment of principal.

解释：

A fixed-rate mortgage provides monthly cash flows that are constant for the whole life of the mortgage. A bond provides semi-annual coupons and a final payment of principal.

固定利率抵押贷款提供的现金流与美国国债提供的现金流有什么区别？ 假设没有提前还款，也没有抵押贷款违约。

固定利率贷款是月现金流，本金摊销到了每月现金流里。

美国国债一般是半年一次的现金流，到期偿还本金与coupon。