Which organization partners with Starbucks to ensure ethical sourcing verification?

The correct answer is Conservation International. This organization partners with Starbucks to enhance its ethical sourcing practices, particularly regarding coffee. Conservation International provides expertise in environmental sustainability and biodiversity, which aligns with Starbucks' commitment to sourcing coffee in a way that supports both the environment and the communities involved in coffee production. Through this partnership, Starbucks can implement standards and verifications that ensure responsible sourcing, which helps to improve the livelihoods of farmers, protect ecosystems, and promote sustainable agricultural practices.

The other organizations, while well-known in the realm of environmental conservation and advocacy, do not have the specific partnership role with Starbucks regarding the verification of ethical sourcing practices that Conservation International does. Consequently, they may work in related areas of environmentalism and sustainability, but their focus does not directly align with the verification of ethical sourcing specifically for Starbucks coffee.