Suppose that $$1$ billion of pass$-$through is used to create a CMO

structure with a PAC bond with a par

value of $$700$ million and a support bond with a par value of $$300$

million. Which of the following will

have the greatest and least average life variability: i$)$ the

collateral, ii$)$ the PAC bond, and iii$)$ the support

bond? Why?