Pardiyono
Pasti bisa TOEFL : oractical strategy for the best scores
Yogyakarta : Andi Offset, 2005,
Buku Teks
Kaplan, Jeffrey P.
English grammar : principles and facts
Prentice Hall International, 1995
Buku Teks SO
Poutsma, H.
Mood and tense of the English verb / H. Poutsma
P. Noordhoff, 1922
Buku Teks SO
Some grammatical errors made by the students of Unpam
Artikel Jurnal
Greenbaum, Sidney
A students grammar of the English language
Longman , 1990
Buku Teks SO