<div class="row">
<div class="col-md-4"><img alt="" src="img url goes here" class="img-fluid mx-auto d-block" /></div>
<div class="col-md-4"><img alt="" src="img url goes here" class="img-fluid mx-auto d-block" /></div>
<div class="col-md-4"><img alt="" src="img url goes here" class="img-fluid mx-auto d-block" /></div>
</div>
EXAMPLE:
