edited by Gareth Williams, Martin Kenyon and Lynn Williams
Overseas Student Trust, 1987
Buku Referensi
Overseas Students Trust , 1987
Buku Teks
Cleveland, Harland, author
McGraw-Hill, 1960
Buku Teks
Brannen, Ted R., author
McGraw-Hill, 1965
Buku Teks
The British Council, 1980
Buku Teks