Bladon, Rachel
Passport Books, [Date of publication not identified]
Buku Teks
Wilkes, Angela
Chicago: A Division of NTC Pub., 1987,
Buku Referensi
Wilkes, Angela
Passport Books, [Date of publication not identified]
Buku Teks SO
Coggle, Paul
Teach Youeself Books, 1991
Buku Teks
Hewitson, Mark
Oxford University Press, 2017
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