大家好请问下面引用的外部实体哪里出错了
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE bookinfo SYSTEM "b.dtd">
<bookinfo>
<book>&nihao;</book>
</bookinfo>
<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT bookinfo (book)>
<!ELEMENT book (#PCDATA)>
<!ENTITY nihao "80.00">