Guptu, Sulekh Chandra
New York, N.Y, Asia Publ. House
Buku Teks
Springer, 2012
eBooks
Dean, Vera Micheles
Rinehart and Winston, 1961
Buku Teks SO
Thakur, Ramesh Chandra
Westview Press, Inc, 1987
Buku Teks SO
Talbot, Phillips
Harper and Brothers, 1958
Buku Teks SO