问为什么这个手风琴不能工作？

EN

    <div class="container">
      <div class="row">
        <div class="col-md-8" id="main">
          <h3>Doesn't it look better ?</h3>
          <div class="panel-group" id="accordion" role="tablist" aria-multiselectable="true">
            <div class="panel panel-default">
              <div class="panel-heading" role="tab" id="headingOne">
                <h4 class="panel-title">
                  <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseOne" aria-expanded="true" aria-controls="collapseOne">
                  Why is it better
                </a>
                </h4>
              </div>
              <div id="collapseOne" class="panel-collapse collapse in" role="tabpanel" aria-labelledby="headingOne">
                <div class="panel-body">
                  <ul>
                    <li>The titles are block, so you don't have to click the text part to activate it</li>
                    <li>Indicators for expand / collapsing items</li>
                    <li>Removed title links' obnoxious :hover underlinings, and outlines.</li>
                  </ul>
                </div>
              </div>
            </div>
            <div class="panel panel-default">
              <div class="panel-heading" role="tab" id="headingTwo">
                <h4 class="panel-title">
                  <a class="collapsed" role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseTwo" aria-expanded="false" aria-controls="collapseTwo">
                  Collapsible Group Item #2
                </a>
                </h4>
              </div>
              <div id="collapseTwo" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingTwo">
                <div class="panel-body">
                Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird
                on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table,
                raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
              </div>
              </div>
            </div>
            <div class="panel panel-default">
              <div class="panel-heading" role="tab" id="headingThree">
                <h4 class="panel-title">
                  <a class="collapsed" role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseThree" aria-expanded="false" aria-controls="collapseThree">
                  Collapsible Group Item #3
                </a>
                </h4>
              </div>
              <div id="collapseThree" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingThree">
                <div class="panel-body">
                Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird
                on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table,
                raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
              </div>
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>