Insert dropdown values with checkbox in php

here is the dropdown image

Cannot insert selected dropdown values with checkbox.It's only inserting the first value of the dropdown in all row.When I click checkbox and click enroll button ,select option doesn't inserting selected value.I have 3 options(Regular,Retake,Recourse) in "examtype" table.So how to insert select option value in database using checkbox?When I click checkbox and click enroll button selected values from dropdown is not inserting.Below is my code.

---

 <?php
if (isset($_POST['enroll']))
{
if (!empty($_POST['chk1'])) 
{
  if (!empty($_POST['et']))
  {
    $roll_no = $_SESSION['roll_no'];
    $selectbox1 = $_POST['et'];
foreach($_POST['chk1'] as $checkbox1)
{
foreach($_POST['et'] as $selectbox1)
$values1 = explode("|", $selectbox1);
$values = explode("|" , $checkbox1);
$course_id= $values[0];
$semester= $values[1];
$course_name= $values[2];
$selectbox1=$values[3];

$sql="INSERT INTO pendingcourse(roll_no,course_id,semester,course_name,exam_type,status) 
VALUES('$roll_no','$course_id','$semester','$course_name','$selectbox1',0)";
$stmt = $connect->prepare($sql);
$stmt->execute();
$checkbox1='';
$selectbox1='';
}
header("location:pending.php");
}
}
}
?>



<form  action="praticadel.php" method="post" enctype="multipart/form-data"> 
<div class="container mt-3" >
    <div class="accordion mb-4" id="accordionExample" >
        <div class="accordion-item" style="background-color: rgb(0, 225, 255);">
          <h2 class="accordion-header" id="headingOne">
            <button class="accordion-button collapsed " type="button" data-bs-toggle="collapse" 
data-bs-target="#collapseOne" aria-expanded="false" aria-controls="collapseOne" 
style="background: #AAFFA9;">
              1st Semester
            </button>
          </h2>
                <table class="table table-bordered border-primary text-center">
                <p> <input type="checkbox" id="selectAll"/>Select All</p>
                    <thead>
                      <tr>
                        <th scope="col-1">Course Id</th>
                        <th scope="col-1">Semester</th>
                        <th scope="col-7">Course</th>
                        <th scope="col-1">Exam Type</th>
                        <th scope="col-1">Select</th>
                         
                      </tr>
                    </thead>
                    <tbody>  
                        

 <?php
 $stmt = $connect->query("SELECT course_id,semester,course_name,seat_available FROM coursetable 
 Where semester = '1st' ");
 $rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
 foreach($rows as $row)
 {
  $course_id = $row['course_id'];
  $semester = $row['semester'];
  $course_name = $row['course_name'];
 ?>
                    <tr>
                        <td scope="row"> <?php echo $course_id?></td>
                        <td > <?php echo $semester ?></td>
                        <td ><?php echo $course_name ?></td>

                        <td>
                        <select name="et[]" id="selectBox" class="form-select form-select-sm" 
    aria-label=".form-select-sm example" onchange="OnSelectionChange">
                        
                        <?php 
                              $stmt1 = $connect->query("SELECT exam_type from examtype");
                              $rows1 = $stmt1->fetchAll(PDO::FETCH_ASSOC);
                              foreach($rows1 as $row1) {
                         ?>
                              <option value="<?php echo $row1['exam_type']; ?>" 
   selected="selected"><?php echo $row1['exam_type']; ?></option>
                         <?php 
                            }
                          ?>
                        </select>
                        </td> 
                        <td>  
                        <input type="checkbox" class="ch" id="checked" onclick="check();" 
   name="chk1[] " value="<?php echo $row['course_id']?>|<?php echo $row['semester']?>|<?php echo 
   $row['course_name']?>|<?php echo $row1['exam_type']?>">
                            <label class="form-check-label" for="flexCheckDefault">
                            </label>  
                        </td>
                      </tr>                     
     <?php
      }
     ?>
                    </tbody>  
              </table>
          </div>
        </div>
      </div>
    </div>
    <div class="container">
  <div class="row">
    <div class="col-md-2 col-xs-6 offset-md-5 mb-3">

    <button type="submit"  name="enroll" class="btn btn-warning mt-2" id="saveChanges"  
    >Enroll</button>
    </div>
  </div>
   </div>
   </form>