php读取xml的问题
我有一个这样的XML文件，我想把question、oid、content都输出，而且输出的格式为：
问题：542
选项：A 内容：1111111
选项：B 内容：2222222
问题：123
选项：C 内容：3333333
选项：D 内容：4444444
应该如何做？

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

<parent>

  <title>3</title>

  <author>admin</author>

  <contentall>

    <subject>

      <question>542</question>

      <option>

        <oid>A</oid>

        <content>1111111</content>

      </option>

      <option>

        <oid>B</oid>

        <content>2222222</content>

      </option>

    </subject>

    <subject>

      <question>123</question>

      <option>

        <oid>C</oid>

        <content>3333333</content>

      </option>

      <option>

        <oid>D</oid>

        <content>4444444</content>

      </option>

    </subject>

  </contentall>

</parent>

------解决方案--------------------

$s =<<< XML

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

<parent>

  <title>3</title>

  <author>admin</author>

  <contentall>

    <subject>

      <question>542</question>

      <option>

        <oid>A</oid>

        <content>1111111</content>

      </option>

      <option>

        <oid>B</oid>

        <content>2222222</content>

      </option>

    </subject>

    <subject>

      <question>123</question>

      <option>

        <oid>C</oid>

        <content>3333333</content>

      </option>

      <option>

        <oid>D</oid>

        <content>4444444</content>

      </option>

    </subject>

  <