function tabbladen(welke) {
	document.getElementById('tab1').className = '';
	document.getElementById('tab2').className = '';
	document.getElementById('tab3').className = '';
	document.getElementById('tabs-content1').className = 'verborgen';
	document.getElementById('tabs-content2').className = 'verborgen';
	document.getElementById('tabs-content3').className = 'verborgen';
	document.getElementById('tab'+welke).className = 'geselecteerd';
	document.getElementById('tabs-content'+welke).className = '';
}