Shepherd, James F.
Houghton Miffiln, 1984
Buku Teks
Gilbert, Doris W.
Prentice-Hall, 1991
Buku Teks SO
Blass, Laurie
McGraw-Hill Publishing Company , 1990
Buku Teks
Cunningham, Sarah
Oxford University Press, 1994
Buku Teks
Cunningham, Sarah
Oxford University Press , 1994
Buku Teks