<!DOCTYPE html><html><head><meta charset="utf-8"><title>菜鸟教程(runoob.com)</title><link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/css/bootstrap.min.css"><script src="https://cdn.staticfile.org/jquery/2.1.1/jquery.min.js"></script><script src="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script></head><body><div class="container"><h2>按...