单标签
<br>
<hr>
<img>
<input>
<param>
<meta>
<link>
双标签
<html>
<head>
<title>
<body>
<table>
<tr>
<td>
<span>
<p>
<form>
<h1>
<h2>
<h3>
<h4>
<h5>
<h6>
<object>
<style>
<b>
<u>
<strong>
<i>
<div>
<a>
<script>
<center>
单标签
<br>
<hr>
<img>
<input>
<param>
<meta>
<link>
双标签
<html>
<head>
<title>
<body>
<table>
<tr>
<td>
<span>
<p>
<form>
<h1>
<h2>
<h3>
<h4>
<h5>
<h6>
<object>
<style>
<b>
<u>
<strong>
<i>
<div>
<a>
<script>
<center>