A bond whose proceeds are used only to finance or refinance a combination of both environmental and social projects is called:

1. A

   Green Bond

   Green Bond: A fixed-income instrument specifically earmarked to raise money for climate and environmental projects only, making it incorrect here since the question specifies a combination of both environmental and social projects.

2. B

   Social Bond

   Social Bond: A bond whose proceeds are exclusively applied to finance or refinance social projects, such as affordable housing or basic infrastructure, which fails to cover the environmental component required by the question.

3. C

   Sustainability Bond

   Sustainability Bond. This bond type finances or refinances a combination of both green (environmental) and social projects, perfectly matching the definition given in the stem.

4. D

   Sovereign Bond

   Sovereign Bond: A debt security issued by a national government in foreign or local currency to fund general government spending, rather than being restricted to specific environmental and social projects.

Summary. Official key is (c). Sustainability bonds uniquely bridge environmental and social domains, whereas green bonds target solely environmental goals, social bonds focus exclusively on social objectives, and sovereign bonds represent general government debt without thematic project restrictions.