Inventors and discoverers : changing our world
National Geographic Book Service
National Geographic Society, 1988
 Buku Referensi
Saaty, Thomas L.
Embracing the future : meeting the challenge of our changing world
Praeger, 1990
 Buku Teks
Garland, John K.
Chemistry of our world
Macmillan, 1975
 Buku Teks
Kolevzon, Edward R.
Our world and its people
Allyn and Bacon, 1959
 Buku Teks
Our world's heritage
National Geographic Book Service.
National Geographic Society, 1987
 Buku Referensi