Rugh, Roberts, author
Burgess , 1971
Buku Teks
Robert, Laurance P., author
Simul Press , 1987
Buku Referensi
King, Gillian M.
Blackwell Scientific Pub., 1982
Buku Referensi
Romer, Alfred Sherwood, author
Saunders College, 1985
Buku Teks
Pough, F. Harvey, author
Prentice-Hall, 1999
Buku Teks