function show_intro(pre,pree,n,select_n,css){for (i = 1; i <= n; i++) {var intro = document.getElementById(pre + i);var cha = document.getElementById(pree + i);intro.style.display = "none";cha.className=css + "2";if (i == select_n) {intro.style.display = "block";cha.className=css + "1";}}}