<script language="javascript">
function show()
{
 for (var i=0;i<document.getElementById("s1").length;i++)
  {for (var j=0;j<document.getElementById("s2").length-1;j++)
     {
 document.getElementById("s2").options.remove(j);
     }
    if (document.getElementById("s1").options[i].selected)
       {show1(document.getElementById("s1").options[i].value);
         break;
       }
    }
}
function show1(v)
{for (var i=1;i<=v;i++)
{
  document.getElementById("s2").options[i]=new Option(i,i);
}
 document.getElementById("s2").options.remove(0);
}
</script>
<select name="s1" onchange="show()" id="s1">
<option value="">请选择</option>
<option value=10>10</option>
<option value=20>20</option>
<option value=30>30</option>
<option value=40>40</option>
</select>
<select name="s2" id="s2">
</select>

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