bootstrap4的轮播图组件为什么插入的图片不能滚动?

bootstrap4这个页面前面已经加载了官方的bootstrap4的CDN的这四个文件

<link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/4.0.0-beta/css/bootstrap.min.css">
<script src="https://cdn.bootcss.com/bootstrap/4.0.0-beta/js/bootstrap.min.js" ></script>
<script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.slim.min.js"></script>
<script src="https://cdn.bootcss.com/popper.js/1.12.3/umd/popper.min.js"></script>

然后带入组件:可版本要是换成3.3.7的就正常了,不知道是哪里出现了问题(求bootstrap4的大神指点1,2)

<div id="carouselExampleIndicators" class="carousel slide" data-ride="carousel">
    <ol class="carousel-indicators">
        <li data-target="#carouselExampleIndicators" data-slide-to="0" class="active"></li>
        <li data-target="#carouselExampleIndicators" data-slide-to="1"></li>
        <li data-target="#carouselExampleIndicators" data-slide-to="2"></li>
    </ol>

    <div class="carousel-inner" role="listbox">
        <div class="carousel-item active">
            <img class="d-block img-fluid" src="./images/1.jpg" alt="First slide">
        </div>
        <div class="carousel-item">
            <img class="d-block img-fluid" src="./images/ribbon.png" alt="Second slide">
        </div>
        <div class="carousel-item">
            <img class="d-block img-fluid" src="./images/2016.png" alt="Third slide">
        </div>
    </div>

    <a class="carousel-control-prev" href="#carouselExampleIndicators" role="button" data-slide="prev">
        <span class="carousel-control-prev-icon" aria-hidden="true"></span>
        <span class="sr-only">Previous</span>
    </a>
    <a class="carousel-control-next" href="#carouselExampleIndicators" role="button" data-slide="next">
        <span class="carousel-control-next-icon" aria-hidden="true"></span>
        <span class="sr-only">Next</span>
    </a>
</div>