Commercial paper is an unsecured, short-term promissory note issued by a corporation to finance short-term liabilities like accounts receivable. Its creditworthiness depends entirely on the financial health and reputation of the issuing corporation. Unlike other money market instruments, it is not guaranteed by a bank or backed by the full faith and credit of a government. This lack of security or guarantee makes it the riskiest option among the choices provided, as investors face the direct credit risk of the corporate issuer.

A. Bankers' Acceptances are guaranteed by a major chartered bank, making their credit risk very low.

C. Treasury Bills are issued by the federal government and are considered the safest money market instrument, with virtually no credit risk.

D. Municipal Short-Term Paper is issued by municipalities and is generally considered to have very low credit risk, second only to federal government debt.

- Canadian Securities Institute. (2022). Investment Funds in Canada Course, Chapter 8: Fixed-Income Securities. The chapter details the features and risks of money market instruments, identifying commercial paper as having higher credit risk than government or bank-guaranteed securities.

- Fabozzi, F. J. (2015). The Handbook of Fixed Income Securities (9th ed.). McGraw-Hill Education. Chapter 11 discusses the various types of money market instruments and their relative credit risks.