function bar(a){
	var sMultimedia = document.getElementById("sMultimedia").getElementsByTagName("dd");
	var sWeb = document.getElementById("sWeb").getElementsByTagName("dd");
	var sBook = document.getElementById("sBook").getElementsByTagName("dd");
	if(a==1){
		var len = sMultimedia.length;
		for (var i =0; i<len ;i++ ){sMultimedia[i].style.display = 'block';}
		}
	else if(a != 1){var len = sMultimedia.length;
		for (var i =0; i<len ;i++ ){sMultimedia[i].style.display = 'none';}
		}
	if(a==2){
		var len = sWeb.length;
		for (var i =0; i<len ;i++ ){sWeb[i].style.display = 'block';}
		}
	else if(a!=2){var len = sWeb.length;
		for (var i =0; i<len ;i++ ){sWeb[i].style.display = 'none';}
		}
	if(a==3){
		var len = sBook.length;
		for (var i =0; i<len ;i++ ){sBook[i].style.display = 'block';}
		}
	else if(a!=3){var len = sBook.length;
		for (var i =0; i<len ;i++ ){sBook[i].style.display = 'none';}
		}	

}