Mortgage-Backed Securities Often Have Payment Patterns That Are "Doubly Convex

Mortgage-backed securities often have payment patterns that are "doubly convex," which means

A) the contract is very complex.
B) that significant changes in the level of interest rates, up and down, produces losses for the investor.
C) that conventional mortgages have double the default risk than other types of mortgages.
D) that investors are exposed to both interest rate risk and default risk.