function tab(id){
		  if(id==1){
		    document.getElementById('tab_1').className="tab_selected";
		    document.getElementById('tab_2').className="tab_normal";
		    document.getElementById('tab_3').className="tab_normal";
			document.getElementById('tab_1c').style.display="block";
			document.getElementById('tab_2c').style.display="none";
			document.getElementById('tab_3c').style.display="none";
			}
		  else if(id==2){
		    document.getElementById('tab_1').className="tab_normal";
		    document.getElementById('tab_2').className="tab_selected";
		    document.getElementById('tab_3').className="tab_normal";
			document.getElementById('tab_1c').style.display="none";
			document.getElementById('tab_2c').style.display="block";
			document.getElementById('tab_3c').style.display="none";
		  }
		  else if(id==3){
		    document.getElementById('tab_1').className="tab_normal";
		    document.getElementById('tab_2').className="tab_normal";
		    document.getElementById('tab_3').className="tab_selected";
			document.getElementById('tab_1c').style.display="none";
			document.getElementById('tab_2c').style.display="none";
			document.getElementById('tab_3c').style.display="block";
		  }
   }