cms.dru.ac.thcms.dru.ac.th/jspui/bitstream/123456789/1337/5/Unit 1.pdf · 1. 2. 3. 4. 5. 6. 7. 1.1 cnu 18 mumjnmnî muäflfl011nîíu mucrmumamumn 3. munifil)J00