求助，很简单的C#问题

老师要求做一个成绩管理系统，要求实现分类登入，可是这个cheng'xu如果用户是学生，即使comboBox不选学生也能顺利登入，admin就没这个问题，请教大佬是为什么？

private void button1_Click(object sender, EventArgs e)
    {
        string sUser = txtUser.Text.ToString();
        string sPassword = txtPassword.Text.ToString();

        if (sUser == "admin" && sPassword == "1234" && comboBoxLeixing.Text == "管理员")
        {
            Menuadmin main = new Menuadmin();
            main.Show();
            this.Hide();
        }

            if (sUser == "徐光睿" || sUser == "曹广" || sUser == "曹子岳" || sUser == "陈思佳" || sUser == "陈旭" || sUser == "黄文广" ||
               sUser == "雷章树" || sUser == "刘晴晴" || sUser == "齐世勐" || sUser == "沈彬" || sUser == "帅兴" || sUser == "孙权伟" ||
               sUser == "王恒" || sUser == "王瑞" || sUser == "向猛" || sUser == "张国梁" || sUser == "张宗友" || sUser == "张舒敏"
               && sPassword == "1234" && comboBoxLeixing.Text == "学生")
            {
                Menustudent main = new Menustudent();
                main.Show();
                this.Hide();
            }

            if (sUser == "刘兆良" || sUser == "龙隆" || sUser == "冯伟" || sUser == "刘善勇" ||
               sUser == "印森林" || sUser == "程乐利" || sUser == "刘岩" || sUser == "赵俊威"
               && sPassword == "1234" && comboBoxLeixing.Text== "教师")
            {
                Menuteacher main = new Menuteacher();
                main.Show();
                this.Hide();
            }

        else
            label3.Text = "用户名或密码错误，请重新输入！";
    }

        if (（sUser == "徐光睿" || sUser == "曹广" || sUser == "曹子岳" || sUser == "陈思佳" || sUser == "陈旭" || sUser == "黄文广" ||
           sUser == "雷章树" || sUser == "刘晴晴" || sUser == "齐世勐" || sUser == "沈彬" || sUser == "帅兴" || sUser == "孙权伟" ||
           sUser == "王恒" || sUser == "王瑞" || sUser == "向猛" || sUser == "张国梁" || sUser == "张宗友" || sUser == "张舒敏"）
           && sPassword == "1234" && comboBoxLeixing.Text == "学生")
                        多打一对括号，如果没猜错，你的教师登陆也是这样，只要sUSer输对了，直接跳转界面了
                        ||：这个符号是左右两边只要有一个满足就进入下一步了
                        &&：这个是两边都满足