Click items in select box, and then display a text input
<p>Now i have a select box. </p>

<pre><code>&lt;select multiple size="5" name="interest"&gt;
 &lt;optgroup label="Sports"&gt;
  &lt;option value=""&gt;Footaball&lt;/option&gt;
  &lt;option value=""&gt;Basketball&lt;/option&gt;
  &lt;option value=""&gt;Volleyball&lt;/option&gt;
 &lt;/optgroup&gt;
 &lt;optgroup label="Music"&gt;
  &lt;option value=""&gt;Folk Musique&lt;/option&gt;
  &lt;option value=""&gt;Pop Musique&lt;/option&gt;
  &lt;option value=""&gt;Rock Musique&lt;/option&gt;
 &lt;/optgroup&gt;
 &lt;optgroup label="Pets"&gt;
  &lt;option value=""&gt;Dogs&lt;/option&gt;
  &lt;option value=""&gt;Cats&lt;/option&gt;
  &lt;option value=""&gt;Rabbits&lt;/option&gt;
 &lt;/optgroup&gt;
 &lt;option value="other"&gt;other&lt;/option&gt;
&lt;/select&gt;
</code></pre>

<p>I want to click "other", and then displays a text field</p>

<pre><code>&lt;input type="text" name="other_interest" /&gt;
</code></pre>

<p>How can i make it?</p>

<p>Thanks very much. </p>
