materializecssでselectボックスが表示されない時に確認すること

<!-- CSS  -->
<!-- Compiled and minified CSS -->
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/materialize/1.0.0/css/materialize.min.css">
<!-- Compiled and minified JavaScript -->
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/materialize/1.0.0/js/materialize.min.js"></script>


<script>
  $(document).ready(function(){
    $('select').formSelect();
  });
</script>


<select>
(略)
</select>