如何在PHP和Boostrap轮播中使用for循环显示图像

Question

我似乎在使用自举轮播在for循环中显示图像时遇到了问题

<?php
  $message = "";
  if(empty($_GET['id'])) {
    $session->message("<div class='btn sm-warning'>please select an image.</div>");
    redirect_to('list_properties.php');
  } 
  $id      = $_GET['id'];
  $sql     = "SELECT * FROM pictures2 WHERE photograph_id='$id';";
  $photos = Picture::find_by_sql($sql);
?>

for循环不显示图像并且目录没有错误，请问有什么办法可以解决吗？

<div id="carouselExampleIndicators" class="carousel slide mx-auto" data-ride="carousel">
  <ol class="carousel-indicators"> 
    <?php 
    $i = 0;
    for ($a = 2; $a < count($photos); $a++):  
   ?>
   <li data-target="#carouselExampleIndicators" data-slide-to="<?php echo $i; ?>" class="<?php echo $i == 0 ? 'active': ''; ?>"></li>
   <?php 
      $i++;
      endfor;
      ?>
  </ol>
  <div class="carousel-inner">
   <?php 
    $i = 0;
    for ($a = 2; $a < count($photos); $a++):  
   ?>
    <div class="carousel-item <?php echo $i == 0 ? 'active': ''; ?>">
        <?php
           $imageUrl  = "images/".$photos['image'][$a];
        ?>
      <img src="<?php echo $imageUrl; ?>" class="img-thumbnail img-responsive"  alt=""/>
    </div>
    <?php 
      $i++;
      endfor;
    ?>
  </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>