Standards for environmental purchasing are developed by:  A. ISO  B. WFTO  C. EMAS  D. FLO

To determine which organization develops standards for environmental purchasing, let's analyze the options provided:

1. ISO (International Organization for Standardization): ISO develops international standards, including those for environmental management, particularly ISO 14001, which focuses on effective management systems for environmental responsibilities.

2. WFTO (World Fair Trade Organization): WFTO focuses on fair trade practices and promoting fair trade enterprises. While sustainability is a part of their mission, they are not primarily focused on environmental purchasing standards.

3. EMAS (Eco-Management and Audit Scheme): EMAS is a voluntary initiative aimed at companies and other organizations to evaluate, report, and improve their environmental performance. It does include environmental aspects but primarily focuses on auditing and management.

4. FLO (Fairtrade Labelling Organizations): FLO establishes international Fairtrade standards, but like WFTO, their focus is primarily on fair trade rather than specifically on environmental purchasing.

Conclusion

The organization that predominantly develops standards related to environmental management and purchasing is A. ISO.

Final Answer: A. ISO