D is corrent. The requirement is to identify the type of bond issue that will not all mature on the same date. D is corrent because a bond issue that matures in installments at various dates is referred to as a serial bond.
A is incorrect because a debenture is a bond that is not secured by collateral.
B is incorrect because a term bond matures on the same date.
C is incorrect because a sinking fund bond is a bond issue that has a provision to set aside cash to repay the bonds at the maturity date.
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