如果我有以下xml,我想选择包含Ritchie的< author> -node来获取作者的全名：

<books>
    <book isbn='0131103628'>
        <title>The C Programming Language</title>
        <authors>
            <author>Ritchie,Dennis M.</author>
            <author>Kernighan,Brian W.</author>
        </authors>
    </book>
    <book isbn='1590593898'>
        <title>Joel on Software</title>
        <authors>
            <author>Spolsky,Joel</author>
        </authors>
    </book>
</books>