<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<!------ Include the above in your HEAD tag ---------->
<div class="container">
<div class="row">
<div class="visible-lg"><!-- Visible lg For Desktops -->
Ad 1 for PCs
</div><!-- End of Visible lg For Desktops -->
<div class="hidden-lg"><!-- Hidden lg for Ipads, phones etc -->
Ad 2 fo tablets and phones
</div><!-- End of Hidden lg -->
</div> <!-------- end of row -->
</div> <!-- end of container -->
</div>
</div>