Sagan, Carl
Time Incorporated, 1966
Buku Referensi
Artikel Jurnal
Suharto Ladjide
Seskoal Press, 2019
Artikel Jurnal
edited by Edward H. Spicer
Russell Sage Foundation, 1952
Buku Teks
Keenleyside, Anne
W. Ross MacDonald School Resource Services Library, 2015
Buku Teks