无法在Bootstrap的行中居中列

Question

我的连续列有问题。他们在左边：

<div class="container-full"> 
  <hr>
  <div class="row">
    <div class="col-xs-6 col-sm-4 col-md-3 col-lg-2">
      <h2>Promo</h2>
      <pr>Lorem ipsum dolor sit amet enim. Etiam ullamcorper. Suspendisse a pellentesque dui, non felis. Maecenamalesuada elit lectus felis, malesuaultricies. Curabitur et ligula. Ut molestie a, ultricies porta urna. Vestibulum commodo volutpat a, convallis ac, laoreet enim. </pr>
    </div>

    <div class="col-xs-6 col-sm-4 col-md-3 col-lg-2">
      <h2>Promo</h2>
      <pr>Lorem ipsum dolor sit amet enim. Etiam ullamcorper. Suspendisse a pellentesque dui, non felis. Maecenamalesuada elit lectus felis, malesuaultricies. Curabitur et ligula. Ut molestie a, ultricies porta urna. Vestibulum commodo volutpat a, convallis ac, laoreet enim. </pr>
    </div>
  </div>

添加text-center等类没有帮助，也没有添加margin:auto。