Which of the following debt investments is not rated?

Corporate bonds, commercial paper, and company deposits are typically rated by credit rating agencies (CRISIL, ICRA, CARE, etc.) to assess credit quality. Debt mutual funds, however, are not rated themselves - they hold a portfolio of rated securities, but the fund as a product is not assigned a credit rating. The fund's risk is reflected in its portfolio credit quality profile (average credit rating, exposure to lower-rated securities), not through a single rating. Option D is correct because debt mutual funds are not rated like individual debt instruments.