First and foremost let me praise and honor the almighty God for the opportunity and capacity given me realize to my aspiration. I am also greatly indebted for St. virgin marry who have been praying for my success. I would like to express my deep gratitude to my research advisor, Abadi Afera (Assistant Professor), for his continuous advice and professional guidance towards realization of this work. My heartfelt appreciation and great thanks go to my co ¿ advisor, Assefa shemie (MA) for critically reviewing the manuscript and for his continuous professional guide on matters pertinent to this thesis. My special thanks go to my mother, Ymegn Alemu, my sisters , Hayimanote Getenet, Habesha Getenet, Trudel Tefera and my lovely brother Yared Molla for their continuous moral support during the study. I am unlucky to lose my father among us and you are always in my heart and in my prayers, may your soul rests in peace in His paradise. I would like to forward my warm appreciation and great thanks to lap publishing for publishing my book.