Dear my students, the semester is over today. I feel so happy to be with you in those busy but interesting days, thanks for your help, thanks for your hard working ,which exactly promoted my work. There must be shortcomings on me that need you forgive, sincerely. you can contact with me anytime if you have any,any problems...so wish you get a good grades! Look forward to the next semester to be with you , work,study,enjoy,together