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 SO
Keenleyside, Anne
W. Ross MacDonald School Resource Services Library, 2015
Buku Teks SO