table-hover が効かない

<div class="container" style="padding:20px 0">
<table class="table table-striped table-bordered table-hover table-condensed">
     <thead>
          <tr><th>foo</th><th>bar</th></tr>
     </thead>
     <tbody>
          <tr><td>foo1</td><td>bar1</td></tr>
          <tr class=“warning"><td>foo2</td><td>bar2</td></tr>
          <tr><td>foo3</td><td>bar3</td></tr>
     </tbody>
</table>
</div>

table-hoverがなぜかききません。どうしてでしょうか？