What is the fastest way to combine two xml files into one

Question

If I have two string of xml1 and xml2 which both represent xml in the same format. What is the fastest way to combine these together? The format is not important, but I ju

Answer 1

var doc= XDocument.Load("file1.xml");
var doc1= XDocument.Load("file2.xml");
doc.Root.Add(doc2.Root.Elements());