Fowler, A. (2000). The virtuous spiral: A guide to sustainability for non-governmental organisations in international development. Earthscan.
Lua i Stíl Chicago (17ú heag.)Fowler, Alan. The Virtuous Spiral: A Guide to Sustainability for Non-governmental Organisations in International Development. London ; Sterling, VA: Earthscan, 2000.
Lua MLA (8ú heag.)Fowler, Alan. The Virtuous Spiral: A Guide to Sustainability for Non-governmental Organisations in International Development. Earthscan, 2000.
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