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Dyfyniad Arddull ChicagoCunningham, William P. Environmental Science: A Global Concern. Boston: McGraw-Hill, 2003.
Dyfyniad MLACunningham, William P. Environmental Science: A Global Concern. Boston: McGraw-Hill, 2003.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.