如何在c＃中通过XPath读取root属性

XML is

<?xml version="1.0" encoding="utf-8"?>
    <Stock Date="13.11.2013 11:14:13">
      <Assortment>
        <ID>1</ID>
        <Item>NNNNNNNNNNNN</Item>
        <Quantity>12</Quantity>
      </Assortment>
    </Stock>
<?xml version="1.0" encoding="utf-8"?>