12/09/14 22:44:52.58
var x = from q in xml.Descendants("question")
let id = (string)q.Element("correctid")
let qt = (string)q.Element("qtext")
from choice in q.Element("choices").Elements("choice")
where (string)choice.Element("choiceid") == id
select qt + ":" + (string)choice.Element("ctext");
XNamespaceは略