function qiehuan(num){
for(var id = 0;id<=4;id++){
if(id==num){
document.getElementById("qh_con"+id).style.display="block";
document.getElementById("mynav"+id).className="nav_on";
}else{
document.getElementById("qh_con"+id).style.display="none";
document.getElementById("mynav"+id).className="";
}}}