Which of the following is most accurate regarding Mortgage-Backed Bonds (MBBs)?

Select one:

a. Mortgages collateralize MBBs, but are not directly related to the associated cash flows

b. They allow financial intuitions to remove mortgages from their balance sheet

c. MBBs usually have a lower credit rating than the financial institution issuing them

d. They insulate financial institutions from prepayment risk