Untitled

<!DOCTYPE html>
<html>
<head>
    <title>test file</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">
</head>
<body>
    <div class="container">
        <div class="row">
            <div class="col-lg-4 col-sm-6">
                <a href="#">
                    <img src="https://cdn.pixabay.com/photo/2016/03/23/12/53/clock-1274699_960_720.jpg" class="img-thumbnail">
                </a>
            </div>
            <div class="col-lg-4 col-sm-6">
                <a href="#">
                <img src="https://cdn.pixabay.com/photo/2014/06/11/17/00/cook-366875_960_720.jpg" class="img-thumbnail">
                </a>
            </div>
            <div class="col-lg-4 col-sm-6">
                <a href="#">
                <img src="https://cdn.pixabay.com/photo/2016/06/25/12/48/go-pro-1478810_960_720.jpg" class="img-thumbnail">
                </a>
            </div>
            <div class="col-lg-4 col-sm-6">
                <a href="#">
                <img src="images/" class="img-thumbnail imgL">
                </a>
            </div>

        </div>
    </div>

</body>
</html>