function forMac(doc){
	if(navigator.userAgent.indexOf('Mac') >= 0)
	{
		var selects = doc.getElementsByTagName('select');
		var cnt = selects.length;
		for(var i = 0; i < cnt; i++){
			if(selects[i].length <= 0){
				selects[i].options[0] = new Option();
				selects[i].setAttribute('size', 4);
			}
		}
	}
}