amp-form中“selected”属性的修改

<select>
  <option value="option1">Option 1</option>
  <option value="option2" selected>Option 2</option>
  <option value="option3">Option 3</option>
</select>

<input type="radio" name="option" value="option1" selected> Option 1
<input type="radio" name="option" value="option2"> Option 2
<input type="radio" name="option" value="option3"> Option 3

<input type="checkbox" name="option1" value="option1" selected> Option 1
<input type="checkbox" name="option2" value="option2"> Option 2
<input type="checkbox" name="option3" value="option3" selected> Option 3

document.querySelector('option[value="option3"]').selected = true;