[Wordpress] Multi-Option Select Search

Hey, i would like to share a code for Wordpress, it worked for all modern browsers but there a problem that doesn’t work in IE, look this javascript code:

<script type="text/javascript" charset="utf-8">
    function choose (el) {
        search = document.getElementById('search_done');
        search.value = document.getElementById('OptionA').value + " " + document.getElementById('OptionB').value;

<form role="search" method="get" id="searchform" action="<?php bloginfo('siteurl'); ?>">

<select name='' id='OptionA' onchange="choose(this);">
  <option value=''selected='selected'>----</option>
  <option value="Sandwich">Sandwich</option>
  <option value="Hamburger">Hamburger</option>

<select name='' id='OptionB' onchange="choose(this);">
  <option value=''selected='selected'>----</option>
  <option value="Soda">Soda</option>
  <option value="Juice">Juice</option>

   <input type="hidden" id="search_done" value="" name="s" />
   <input type="submit" id="searchsubmit" value="">


I’m not sure how to fix for bad internet browser like IE, but every clients want this so… :confused:

I appreciate to someone who has an idea how to fix this for IE