使用simplexml_load_string()如何从以下XML获取"ForgotPassword"？
<?xml version="1.0" encoding="utf-8"?>
<ForgotPassword>
<version>1.0</version>
<authentication>
<login>username</login>
<apikey>login</apikey>
</authentication>
<parameters>
<emailAddress>joesmith@example.com</emailAddress>
</parameters>
</ForgotPassword>