<input type="radio" NAME="type" id="rbtA"><span id="txtA">Alt. A</span>
<input type="radio" NAME="type" id="rbtB"><span id="txtB">Alt. B</span>
<input type="radio" NAME="type" id="rbtC"><span id="txtC">Alt. C</span>

<input type="radio" NAME="COM" id="rbtSub1"><span id="txtSub1">SubAlt. 1</span>
<input type="radio" NAME="COM" id="rbtSub2"><span id="txtSub2">SubAlt. 2</span>
<input type="radio" NAME="COM" id="rbtSub3"><span id="txtSub3">SubAlt. 3</span>
<input type="radio" NAME="COM" id="rbtSub4"><span id="txtSub4">SubAlt. 4</span>

<input type="radio" NAME="Coupling" id="rbtSubSub1"><span id="txtSubSub1">Yes</span>
<input type="radio" NAME="Coupling" id="rbtSubSub2"><span id="txtSubSub2">No</span>

<SELECT id="selectCom" style="width: 160" NAME="Communication"><OPTION selected="selected"></OPTION></SELECT>

var arraySub1=["1A", "1B", "1C"];
//(correspondingly for sub2 and sub3)...
var arraySub4=["4A", "4B", "4C"];
var mapCom = { rbtSub1 : arraySub1, rbtSub2 : arraySub2, rbtSub3 : arraySub3, rbtSub4 : arraySub4 }

$('#rbtSub1, #rbtSub2, #rbtSub3, #rbtSub4').change(function() {
  $("#selectCom option").remove();
  $.each(mapCom[this.id], function(i, val) {
    var opt = $("<option />");
    opt.appendTo($("#selectCom")).text(val).val(val);
  });
});