php怎样处理xml字符串？

Question

<?xml version="1.0" encoding="utf-8" ?> 
  <string xmlns="http://tempuri.org/">
<NewDataSet> <Results> 
<NewsID>1</NewsID> <Title>a </Title> 
<Content>content a</Content> <NewsDate>2006-02-01T00:00:00.0000000+08:00</NewsDate> </Results> <Results> 
<NewsID>2</NewsID> <Title>b </Title> 
<Content>content b</Content> <NewsDate>2006-02-02T00:00:00.0000000+08:00</NewsDate> </Results> <Results> 
<NewsID>3</NewsID> <Title>c </Title> 
<Content>content c</Content> <NewsDate>2006-02-03T00:00:00.0000000+08:00</NewsDate> </Results> </NewDataSet></string> 以上是返回的xml串，需要把标志中间的内容提取出来