jestem chyba za głupi na to... skopiowałem i nie działa
ehhh... czegoś nie dopisałem albo coś?
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
<script src="jquery.chained.min.js"></script>
</head>
<body>
<script>
$("#series").chained("#mark");
$("#model").chained("#series");
</script>
<form>
<select id="mark" name="mark">
<option value="">--</option>
<option value="bmw">BMW</option>
<option value="audi">Audi</option>
</select>
<select id="series" name="series">
<option value="">--</option>
<option value="series-3" class="bmw">3 series</option>
<option value="series-5" class="bmw">5 series</option>
<option value="series-6" class="bmw">6 series</option>
<option value="a3" class="audi">A3</option>
<option value="a4" class="audi">A4</option>
<option value="a5" class="audi">A5</option>
</select>
<select id="model" name="model">
<option value="">--</option>
<option value="coupe" class="series-3 series-6 a5">Coupe</option>
<option value="cabrio" class="series-3 series-6 a3 a5">Cabrio</option>
<option value="sedan" class="series-3 series-5 a3 a4">Sedan</option>
<option value="sportback" class="a3 a5">Sportback</option>
</select>
</form>
</body>
</html>