基于子值的XPath选择

Here's some xml:

这是一些xml:

<books>
    <book>
        <author>Tom</author>
        <genres>
            <genre>Science</genre>
            <genre>Romance</genre>
        </genres>
    </book>
    <book>
        <author>Mike</author>
        <genres>
            <genre>Politics</genre>
            <genre>Romance</genre>
        </genres>
    </book>
</books>
<books>
    <book