当第二个下拉列表取决于第一个下拉列表选择时，如何创建表单

<form>
  <select id="firstDropdown" onchange="updateSecondDropdown()">
    <option value="option1">Option 1</option>
    <option value="option2">Option 2</option>
    <option value="option3">Option 3</option>
  </select>
  
  <div id="secondDropdownContainer"></div>
  
  <input type="submit" value="Submit">
</form>

<script>
function updateSecondDropdown() {
  var firstDropdown = document.getElementById("firstDropdown");
  var selectedValue = firstDropdown.value;
  var secondDropdownContainer = document.getElementById("secondDropdownContainer");
  
  // 清空第二个下拉列表
  secondDropdownContainer.innerHTML = "";
  
  // 根据第一个下拉列表的选中值创建第二个下拉列表
  var secondDropdown = document.createElement("select");
  secondDropdown.id = "secondDropdown";
  
  // 根据第一个下拉列表的选中值确定第二个下拉列表的选项
  if (selectedValue === "option1") {
    var option1 = document.createElement("option");
    option1.value = "option1-1";
    option1.innerHTML = "Option 1-1";
    secondDropdown.appendChild(option1);
    
    var option2 = document.createElement("option");
    option2.value = "option1-2";
    option2.innerHTML = "Option 1-2";
    secondDropdown.appendChild(option2);
  } else if (selectedValue === "option2") {
    var option3 = document.createElement("option");
    option3.value = "option2-1";
    option3.innerHTML = "Option 2-1";
    secondDropdown.appendChild(option3);
    
    var option4 = document.createElement("option");
    option4.value = "option2-2";
    option4.innerHTML = "Option 2-2";
    secondDropdown.appendChild(option4);
  } else if (selectedValue === "option3") {
    var option5 = document.createElement("option");
    option5.value = "option3-1";
    option5.innerHTML = "Option 3-1";
    secondDropdown.appendChild(option5);
    
    var option6 = document.createElement("option");
    option6.value = "option3-2";
    option6.innerHTML = "Option 3-2";
    secondDropdown.appendChild(option6);
  }
  
  // 将第二个下拉列表添加到容器中
  secondDropdownContainer.appendChild(secondDropdown);
}

// 在提交时执行相应的操作
document.querySelector("form").addEventListener("submit", function(event) {
  event.preventDefault();
  
  // 处理表单提交的逻辑
});
</script>