อ้างอิง

1.http://www.eco.ru.ac.th/eco/sar/4_52/4.4/4_4_1_22.pdf

2.http://www.gsb.or.th/100anniversary/evolution/section-04.php

3.http://student.nu.ac.th/may/lesson3.htm

4.http://www.matichon.co.th/online/2010/07/12795331741279533210l.jpg

5.http://journalmwu.files.wordpress.com/2011/03/05.jpghttp://www.bloggang.com/data/mr-cozy/picture/1187061431.jpg

6.http://www.2519.net/newweb/gallery_new/images/5/WedDecember2003-18-6-16-big5.jpghttp://3.bp.blogspot.com/_ve0wHBk3A0I/S9LV37uza7I/AAAAAAAAKz0/bXjlqhtxkjg/s400/15.jpg

7.http://www.oknation.net/blog/home/user_data/file_data/201310/06/2001f45b.jpghttp://www.2519.net/newweb/gallery_new/images/5/WedDecember2003-18-6-16-big2.jpg

8.http://www.oknation.net/blog/home/blog_data/121/121/images/84/00.jpg

9.https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjF4K87Xzm5VAfiikpdoua99q8SFYxHUeefxbr5dYM9_TaNjT6CAlZ16DNCCP7NiYyNB3Fd1l7lLq8XZBcQ87TnPoc_hH2xAqUXMnIAPaN8nD_oUVi_J7gYH_1jR10LyE-2_JPIpTc0mQI/s1600/6tula2519-5.jpg

10.http://www.oknation.net/blog/home/blog_data/44/44/images/6oct2.jpg