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<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>W3Cschool教程(w3cschool.cn)</title>
<body>
<p id="Demo">段落 1。</p>
<p id="demo">段落 2。</p>
<script>
// 只有段落 2 会被替换
document.getElementById("demo").innerHTML = "HELLO。";
</script>
</body>
</html>