nth-child returning source, not the expected target(s) : I'm trying to sharpen my jQuery skills by learning to use `nth-child` selector but with little luck.  I'm sure I'm just doing something slightly wrong, and I will have a follow up question to this again regarding nth-child, so any help is appreciated.

I would have thought my code below would have select "Saab" and "Audi" in the pulldown menu, but what it does is return the "source" `select` element, `select#carsmenu`.  What am I doing wrong?   

    <script>
      $(document).ready(function() {
          console.log($('#carsmenu:nth-child(odd)').prop('selected', true));
      });
    </script>  
    
    <select multiple id="carsmenu">
      <option value="volvo">Volvo</option>
      <option value="saab">Saab</option>
      <option value="mercedes">Mercedes</option>
      <option value="audi">Audi</option>
    </select>