Código:
  
<script>
function mostrar(numero)
{
document.getElementById('numero')style.visibility='visible';
}
</script>
<form>
<select name=11 id=0  onChange="mostrar(1)" >
<option > 1</option>
<option > 1</option>
</select>
<select name=2 id=1 onChange="mostrar(this.id)">
<option > 1</option>
<option > 1</option>
</select>
</form>
 
 
