Marriot, Bety Bowers
McGraw-Hill, 1997
Buku Referensi
Eccleston, Charles H.
CRC Press, Taylor & Francis Group, 2011
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Unesco-Unep International Environment Education Programme. National Institute of Educational Planning and Administration , 1988
Buku Teks
National Institute of Educational Planning and Administration , 1985
Buku Teks
Anjaneulu, Y.
BS Publication, 2011
Buku Teks SO