bootstrap怎么使图片垂直居中？
<div class="mbrand"> <a href="#"><img src="img/mbarnd1.gif" class="img-responsive center-block"/></a> <a href="#"><img src="img/mbarnd2.gif" class="img-responsive center-block"/></a> <a href="#"><img src="img/mbarnd3.gif" class="img-responsive center-block"/></a> <a href="#"><img src="img/mbarnd4.gif" class="img-responsive center-block"/></a> <a href="#"><img src="img/mbarnd5.gif" class="img-responsive center-block"/></a> </div>
把图片添加css类img-responsive center-block