VanHuss, Susie H.
South-Western Education Publishing, 1998
Buku Teks
Hutabarat, Roselyne
Erlangga, 2009
Buku Teks
Keenan, John
John Wiley & Sons, 1982
Buku Teks
King, F.W
Longmans , 1979
Buku Teks
Bowman, Joel P.
Harper & Row Publishers, 1979
Buku Referensi