B. Protective clauses in bond indentures are not called "requirements." This is not a defined term for a bond indenture.

C. The "provisions" of a bond indenture are the terms of the bond. The include the issuer’s obligations to the bond holders. They may or may not be protective clauses.

D. Covenants are restrictions on the issuer included in a bond indenture that preserve the company's financial solvency and thus its ability to repay the debt. They provide protection to the holder of the bond, so they are known as "protective covenants." Covenants may include a requirement that the issuer maintain a certain minimum level of working capital, limitation on capital expenditures, limitation on other indebtedness, or other requirements.