<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Responsive Bootstrap Grid</title>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<div class="container">
<h1 class="text-center my-4">Responsive Bootstrap Grid Example</h1>
<div class="row">
<div class="col-md-4 col-sm-6 mb-4">
<div class="card">
<div class="card-body">
<h5 class="card-title">Column 1</h5>
<p class="card-text">Content for column 1. This column is responsive.</p>
</div>
</div>
</div>
<div class="col-md-4 col-sm-6 mb-4">
<div class="card">
<div class="card-body">
<h5 class="card-title">Column 2</h5>
<p class="card-text">Content for column 2. This column is responsive.</p>
</div>
</div>
</div>
<div class="col-md-4 col-sm-12 mb-4">
<div class="card">
<div class="card-body">
<h5 class="card-title">Column 3</h5>
<p class="card-text">Content for column 3. This column is responsive.</p>
</div>
</div>
</div>
</div>
</div>
<script src="https://code.jquery.com/jquery-3.5.1.slim.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/@popperjs/core@2.9.3/dist/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"></script>
</body>
</html>