请老师检查，谢谢！

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title></title>
    <style>
        body {
            background: #f3f3f3;
        }
       /*此处补充代码*/
       .div_1{
           width:200px;
           height:100px;
           border:5px solid red;
           border-radius:0px 50px 20px 50px / 0px 50px 40px 50px;
       }
       .div_2{
           width:100px;
           height:200px;
           margin-top:20px;
           border:5px solid red;
           border-radius:10px 50px 100px 10px;
       }
       .div_3{
           width:100px;
           height:200px;
           margin-top:20px;
           border:5px solid red;
           border-radius:10px 40px 10px 40px;
           
       }
    </style>
</head>

<body>
   <!--此处补充代码-->
   <div class="div_1"></div>
   <div class="div_2"></div>
   <div class="div_3"></div>
</body>
</html>

努力的刘同学 2020-02-29

源自：项目：CSS3实现汉克狗案例 2-13 编程练习