Which of the following choices correctly places callable bonds, straight coupon bonds, mortgage-backed securities, and zero-coupon bonds in order from the type of security with the least reinvestment risk to the one with the most reinvestment risk（）
A. zero-coupon bonds, mortgage-backed securities, straight coupon bonds, callable bonds.
B. zero-coupon bonds, straight coupon bonds, callable bonds, mortgage-backed securities.
C. mortgage-backed securities, zero-coupon bonds, callable bonds, straight coupon bonds.
