So GD&DT Hai Phong Digitally signed by So GD&DT Hai Phong DN: cn=So GD&DT Hai Phong c=VN l=Hai Phong o=So GD&DT Hai Phong ou=So GD&DT Hai Phong e=vanphong@haiphong.edu.vn Reason: I am the author of this document Location: Date: 08/16/11 08:59:58