Environmental ValuesArchived 2017-03-06 at the Wayback Machine, based on Singer, Peter "The Environmental Challenge", Ian Marsh, edit., Melbourne, Australia: Longman Cheshire, 1991, 0-582-87125-5. pp. 12
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Environmental ValuesArchived 2017-03-06 at the Wayback Machine, based on Singer, Peter "The Environmental Challenge", Ian Marsh, edit., Melbourne, Australia: Longman Cheshire, 1991, 0-582-87125-5. pp. 12