function qiehuan(num){
  for(var id = 0;id<=7;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="";
   }
  }
 }