源代码 ：
点击运行
<!DOCTYPE html> <html> <head> <title>Bootstrap 实例</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/4.3.1/css/bootstrap.min.css"> <script src="https://cdn.staticfile.org/jquery/3.2.1/jquery.min.js"></script> <script src="https://cdn.staticfile.org/popper.js/1.15.0/umd/popper.min.js"></script> <script src="https://cdn.staticfile.org/twitter-bootstrap/4.3.1/js/bootstrap.min.js"></script> </head> <body> <div class="container"> <h2>表单控件: select</h2> <p>以下表单包含了两个下拉菜单 (select 列表):</p> <form> <div class="form-group"> <label for="sel1">单选下拉菜单:</label> <select class="form-control" id="sel1"> <option>1</option> <option>2</option> <option>3</option> <option>4</option> </select> <br> <label for="sel2">多选下拉菜单(按住 shift 键，可以选取多个选项):</label> <select multiple class="form-control" id="sel2"> <option>1</option> <option>2</option> <option>3</option> <option>4</option> <option>5</option> </select> </div> </form> </div> </body> </html>
运行结果