The completion of this thesis could not have been possible without the participation and assistance of so many people whose names may not all be enumerated. Their contributions are sincerely appreciated and gratefully acknowledged. However, I would like to express my deep appreciation and indebtedness particularly to the following: Dr. Mohammad Falahat, supervisor, for his support, advice, guidance, valuable comments, suggestions, and provisions that benefited me much in the completion and success of this study. I am also appreciated him for sharing his knowledge and helped in the analysis of data and its statistical computations. And lastly by giving an endless helped to finish this thesis. To all relatives, friends and others who in one way or another shared their support, either morally, financially and physically, thank you. vi