Comment utiliser la balise select en HTML

<select>
     <option value="=1">上海</option>
     <option value="=2" selected="selected">北京</option>
     <option value="=3">广州</option>
</select>

 <select size="3">
       <option>上海</option>
       <option>广州</option>
       <option>深圳</option>
 </select>
  
 <select multiple="multiple" size="3">
       <option>上海</option>
       <option>广州</option>
       <option>深圳</option>
 </select>

<select>
      <optgroup label="河北省">
          <option>石家庄</option>
          <option>邯郸</option>
          <option>枣阳</option>
      </optgroup>
      <optgroup label="湖北省">
          <option>武汉</option>
          <option>咸宁</option>
          <option>赤壁</option>
      </optgroup>
      <optgroup label="河南省">
          <option>郑州</option>
          <option>安阳</option>
          <option>驻马店</option>
      </optgroup>
</select>