//数据预测  导航
        var totalItems = 5; //一级菜单的个数
        var level1Prefix = "pc-"; //一级菜单id的前缀
        var level2Prefix = "pcs-"; //二级菜单id的前缀

        function swapItem(num) {
            for (var id = 1; id <= totalItems; id++) {
                if (id == num) {
                    document.getElementById(level2Prefix + id).style.display = "block";
                    document.getElementById(level1Prefix + id).className = "projections-nav_on";
                } else {
                    document.getElementById(level2Prefix + id).style.display = "none";
                    document.getElementById(level1Prefix + id).className = "";
                }
            }
        }