DECLARATION OF ORIGINALITY I am Nguyen Xuan Dung, PhD student of Course 23, Academic Year 2019 - 2022, hereby declare that the research work is entirely my own original work under the guidance and supervision of Assoc. Prof., Dr.Nguyen Duc Trung. I affirm that this work has not been previously submitted to any other institution or organization for any academic or professional qualification. I acknowledge and properly cite all the sources used in this work, ensuring that all information, data, and materials are accurate, reliable, and appropriately referenced. I take full responsibility for the authenticity, originality, and integrity of the content presented in this work. Ho Chi Minh City, day month year Author i Powered by TCPDF (www.tcpdf.org)