Ritsema, Beatrijs
Promotheus, 1993
Buku Teks
Study Rizal L.K., author
Artikel Jurnal
edited by Howard L. Parad and Roger R. Miller
Family Service Association of America, 1968
Buku Teks
R. A. F.
Rahmat Cijulang, 1991
Buku Teks
Rand, Ayn, author
Ikon Teralitera, 2003
Buku Teks