3-3一样的代码，为什么我的会报错

hr.xml

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hr SYSTEM "hr.dtd">

<!-- 人力资源管理系统 -->

<hr>

<employee no="3301">

<name>李铁柱</name>

<age>37</age>

<salary>3600</salary>

<department>

<dname>人事部</dname>

<address>XX大厦-B105</address>

</department>

</employee>

</hr>

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hr.dtd

<?xml version="1.0" encoding="UTF-8"?>

<!ELEMENT hr (employee)>