function showa(a)
{
	 
	var divshowname =new Array("content_a","content_a1","content_a2","content_a3","content_a4","content_a5","content_a6");
	for( var i=0;i<7;i++){
		 
	if (a==divshowname[i]){
		document.getElementById(divshowname[i]).style.display ='block';
		}else{
         document.getElementById(divshowname[i]).style.display ='none';
}
}
}