bootstrap 下面的三个圆圈需要点击才能切换图片，如果设置为鼠标移动到3个圆圈上就切换图片

Question

<div id="demo" class="carousel slide" data-ride="carousel">

<!-- 指示符 -->
<ul class="carousel-indicators">

<li data-target="#demo" data-slide-to="0" class="active"></li>
<li data-target="#demo" data-slide-to="1"></li>
<li data-target="#demo" data-slide-to="2"></li>

</ul>

<!-- 轮播图片 -->
<div class="carousel-inner">

<div class="carousel-item active">
  <img src="https://static.runoob.com/images/mix/img_fjords_wide.jpg">
</div>
<div class="carousel-item">
  <img src="https://static.runoob.com/images/mix/img_nature_wide.jpg">
</div>
<div class="carousel-item">
  <img src="https://static.runoob.com/images/mix/img_mountains_wide.jpg">
</div>

</div>

<!-- 左右切换按钮 -->

<span class="carousel-control-prev-icon"></span>

<span class="carousel-control-next-icon"></span>

</div>