Marcella, Rita, author
Gower ; Jaico Publishing House,
Buku Referensi
Chan, Lois Mai, author
McGraw-Hill, 1994
Buku Teks
Batley, Sue, author
Chandos, 2005
Buku Teks
Sayers, W.C. Berwick, author
Deutsch, 1967
Buku Teks
Benson, Lyman, author
D.C. Heath , 1957
Buku Teks