function renewDateOfBirth(month, year, select) {	
	var last_day = 31;
	
	if (month == 2) {
		last_day = 29;
	} else if (month == 4 || month == 6 || month == 9 || month == 11) {
		last_day = 30;
	}
	
	for (i = select.options.length - 1; i >= 0; i--) {
		select.remove(i);
	}
	
	select.options[0] = new Option('Dag:', '-');
	for (i = 1; i <= last_day; i++) {
		select.options[i] = new Option(i, i);
	}
}