Submitted By:

First my thankfulness be to Allah, the Almighty, without whose help, I wouldn't have accomplished this work. I would like also to thank my supervisor, Dr. Abdalla Yassin for his invaluable supervision, support and encouragement which paved my way and guided me to the right path. Iam also grateful to my friend Dr.Ahmed Taha and DR. Abd-AL Gadir Mohammad Ali who guided me and explained to me the early stages of the scientific research. Iam also grateful to my wife for her kind co-operation and valuable ideas. I have had a great deal of help and feedback from many people in writing this research. Among them the teacing staff of Sudan Unieversity of Science & Technology, who participated in the empirical part of this study. I am also indebted to linda, Mr.Mohamed Al Ameen, and Dr.Aymen El Sheikh, who supplied a lot of materials needed for the research. My thanks also go to Ms. Michel, who offered a lot of time and help