<table>元素用来创造表格，表格的内容进行编写。你需要用起始标签来表示每行的开始。
<!DOCTYPE html>
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<html>
<head>
<title>TODO supply a title</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<div>表格的结构</div>
<table>
<tr>
<td>15</td>
<td>15</td>
<td>30</td>
</tr>
<tr>
<td>45</td>
<td>60</td>
<td>45</td>
</tr>
<tr>
<td>60</td>
<td>90</td>
<td>90</td>
</tr>
</table>
</body>
</html>