function service() {
    var teacherService = document.getElementById("teacherService");
    var studentService = document.getElementById("studentService");
    var tServiceLi = document.getElementById("tServiceLi");
    var sServiceLi = document.getElementById("sServiceLi");
    tServiceLi.style.display = "none";
    sServiceLi.style.display = "none";
    teacherService.onclick = function() {
        sServiceLi.style.display = "none";
        if (tServiceLi.style.display == "none") {
            tServiceLi.style.display = "block"; return false;
        }
        if (tServiceLi.style.display == "block") {
            tServiceLi.style.display = "none";
        }

    }
    studentService.onclick = function() {
        tServiceLi.style.display = "none";
        if (sServiceLi.style.display == "none") {
            sServiceLi.style.display = "block"; return false;
        }
        if (sServiceLi.style.display == "block") {
            sServiceLi.style.display = "none";
        }

    }


}
addLoadEvent(service);