Sustainability Bonds are fixed-income instruments where the proceeds are exclusively applied to finance or re-finance a combination of both environmental (green) and social projects.

Green Bonds are specifically earmarked to raise money exclusively for climate and environmental projects (e.g., renewable energy, pollution prevention, biodiversity conservation).

Social Bonds raise funds exclusively for projects that address or mitigate a specific social issue and seek to achieve positive social outcomes (e.g., affordable basic infrastructure, access to essential services, affordable housing).

Sovereign Bonds refer to debt securities issued by a national government to finance general government spending and manage national debt. The term refers to the issuer rather than the specific use of proceeds, meaning a standard sovereign bond is not inherently restricted to environmental or social projects.

Therefore, the correct option is C.