add SELECT in searchform.php

Hi, I’m trying to change the searchform adding select tags.
In Hueman if i search “a b c” the search result in the url is “/?s=a+b+c”, but with the new form I am not able to print the sum.

How can i solve?

This is the code:

<form role="search" method="get" id="searchform" action="<?php echo home_url( '/' ); ?>">
<label>
<select name="s" id="s">
<option value="nessuno">choose</option>
<option value="a">a</option>
<option value="b">b</option>
<option value="c">c</option>
</select>
</label>
<label>
<select name="s" id="s">
<option value="nessuno">choose</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</label>
<label>
<input type="submit" id="searchsubmit" value="Search" />
</label>
</form>

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