<form action="./02_demo.php" method="post" enctype="multipart/form-data">
账号: <input type="text" value="jack" name="username" placeholder="请输入账号"><br>
密码: <input type="password" value="123456" name="userpwd" placeholder="请输入账号"><br>
性别: 男<input type="radio" name="sex" value=