Explanation

Based on the provided text, the corporate trustee "acts in a fiduciary (legal) capacity on behalf of the investors" and "acts on behalf of the bondholders."

Key points from the text:

• The corporate trustee is a third party to the contract
• Acts in a fiduciary capacity on behalf of the investors
• Represents the bondholders
• Ensures the bond issuer complies with the covenants

Analysis of options:

• I. bond investors ✓ Correct - The trustee acts on behalf of investors/bondholders
• II. bond issuers ✗ Incorrect - The trustee monitors the issuer, doesn't represent them
• III. bond underwriters ✗ Incorrect - Underwriters are involved in issuance but not represented by the trustee
• IV. regulators ✗ Incorrect - The trustee is not a regulatory body

Therefore, the corporate trustee acts in a fiduciary capacity only for bond investors, making option A ("I only") the correct answer.