public void GetAllTeacherByDepartment()
        {
            Teachers _Teachers = new Teachers();

            _Teachers.DepartmentId             = Convert.ToInt32(DepartmentDropDownList.SelectedValue);
            TeacherDropDownList.DataSource     = _CourseAssigneManager.GetAllTeacherByDepartment(_Teachers.DepartmentId);
            TeacherDropDownList.DataTextField  = "TeacherName";
            TeacherDropDownList.DataValueField = "Id";
            TeacherDropDownList.DataBind();
            TeacherDropDownList.Items.Insert(0, new ListItem("Select Teachers", "0"));
        }