[danik.js]

Задача для детсада )

<select id="sel" name="sel"> 
    <option value="1">First</option> 
    <option value="2">Second</option> 
</select> 

<select id="select_1" name="sel"> 
    <option id="element_1" value="a">a</option> 
    <option id="element_2" value="b">b</option> 
</select> 

<select id="select_2" name="sel"> 
    <option id="element_1" value="c">c</option> 
    <option id="element_2" value="d">d</option> 
</select> 

<select id="select_3" name="sel"> 
    <option id="element_1" value="e">e</option> 
    <option id="element_2" value="f">f</option> 
</select>
<script>
(function(){
    var master = document.getElementById('sel'),
        slaves = [];

    for (var i = 0; i < 3; i++) {
        slaves[i] = document.getElementById('select_' + (i + 1));
    }

    master.onchange = function() {
        for (var i = 0; i < 3; i++) {
            slaves[i].selectedIndex = this.value - 1;
        }
    }
})();
</script>