我正在使用col-xs-6 col-md-3分区但是当我到达第6行时，项目的位置向右摇摆可以请任何人帮我纠正这个问题。
块引用
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/fishoil.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Fish Oil</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/jympre.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Jym</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/supercharge.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Super Charge</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/arnoldironmass.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Arnold Mass</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/mass-tech.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Mass Tech</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/upyourrmass.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Up Your Mass</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/goldwhey.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Whey Protein</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/c4big.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>C4</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/animalpump.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Animal Pump</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/celltech.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Cell Tech Creatine</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/platinumcreatine.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Platinum Creatine</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/dailyformula.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Daily Formula</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/seriousmass.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Serious Mass</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/truemass.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>True Mass</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/cellmass.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>True Mass</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/carnivor.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Carnivor Protein Bar</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/combatcrunch.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Combat Crunch Bar</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/universalprotein.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Universal Hi Protein Bar</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/hydroxycut.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Hydroxycut</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/hydroxycut.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Hydroxycut</h3>
</div>
</div>
</div>
<div class="col-xs-6 col-md-3">
<div class="portfolio-item">
<img class="img" src="img/png/hydroxycut.png" alt="" style="width: 200px; height:200px" />
<div class="caption">
<h3>Hydroxycut</h3>
</div>
</div>
</div>
我问了这个问题，因为这是我第一次面对这个问题和其他参考文献..因为被问到的问题已经没有真正回答我的问题