Select the most appropriate term from within the parentheses:
a. (High-grade utility bonds/Low-grade industrial bonds) generally have only light sinking-fund requirements.
b. Collateral trust bonds are often issued by (utilities/industrial holding companies).
c. (Utility bonds/Industrial bonds) are usually unsecured.
d. Equipment trust certificates are usually issued by (railroads/financial companies).
e. Mortgage pass-through certificates are an example of (an asset-backed security/project finance).