Answer: b. debenture bonds.
Step-by-step explanation:
A debenture bond is a debt instrument that is unsecured by a collateral or asset. They are issued by companies to raise capital.
A callable bond is a bond that can be redeemed before its maturity date.
A junk bond is a very risky bond with low credit ratings but pay a higher yield when compared to better rated bonds.
Indebenture bond is a legal document that describes the features and terms of a bond.