The completion of the paper is due to the information and knowledge of the professors in the Suzhou Agricultural Carrer Technique College. Under their help, I have accumulated all the demanding knowledge for his paper. I also benefited from my advisor Prof. Li. Prof. Li helped me with comfiming the topic and frame, collecting informations, preparing the opening report and the draft. Prof. Li made great effort in choosing words and phrases in the draft of my paper. Thanks again for Prof. Li's taking his time to help also appreciate all the faculties who had given me help and advice during my four years in the university. I will never forget the advice my head-teacher Mr. Yang gave me. I also appreciate all the professors who have informed me of all the information I needed for my major during the fours years period in the that, I want to say thank you to my roomates who had been living with me during the four years. They brought me happiness and comfort to my campus life. I hope all our future life would be full of substance and my classmates have been helping me with the materials of different courses. They are all very warm-hearted. They helped me not only in school work, but also in daily life. We are friends not only classmates. I do appreciate their back to my long way in studying, my parents gave me the greatest encouragement. They supported me for my tuition fees. They also tolerated the missing of their child. I can see the delight in their eyes when I am going back home. I can also feel the reluctance in their eyes when I am leaving for school. Their words in the phone contains a strong emotion of missing and expectation. I know I have to study very hard. Except for the good grade, I can not find anything else to pay for them. I hope they can be consoled in my further study, carrer and life.