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Dyfyniad Arddull ChicagoEngelman, Robert, and Pamela LeRoy. Sustaining Water: Population and the Future of Renewable Water Supplies. Washington: Population Action International, 1993.
Dyfyniad MLAEngelman, Robert, and Pamela LeRoy. Sustaining Water: Population and the Future of Renewable Water Supplies. Washington: Population Action International, 1993.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.