1. English Course III, Unit 2, by Asst. Prof. Chorthip Viriya, Thammasat University, May 2005
2. English Course III, by Asst. Prof. Virasuda Sribayak, Thammasat University, May 2005)
3. http://www.englishclub.com/esl-exams/ets-toeic-practice-7.htm
4. REPARATION SERIES FOR THE NEW TOEIC TEST, Advanced Course, Fourth Edition, Lin Lougheed, Pearson Education, Inc. 2007 page 176
5. http://www.englishclub.com/esl-exams/ets-toeic-practice-7.htm
6. http://www.usingenglish.com/comprehension/13.html
