Concatenating Environment.CurrentDirectory with back path

string path = Environment.CurrentDirectory + @"....Project2xmlFile.xml":

string path = System.IO.Path.Combine(Environment.CurrentDirectory,
                                     @"......Project2xmlFile.xml");

System.IO.Path.GetFullPath(@"....Project2xmlFile.xml")

string path = Path.Combine( Environment.CurrentDirectory,
                            @"......Project2xmlFile.xml" );

string path = System.IO.Path.Combine(@"c:dir1dir2",
                                     @"....Project2xmlFile.xml");

@"c:dir1dir2dir3....Project2xmlFile.xml"

public static string CombinePaths(string rootPath, string relativePath)
{
    DirectoryInfo dir = new DirectoryInfo(rootPath);
    while (relativePath.StartsWith("..\"))
    {
    	dir = dir.Parent;
    	relativePath = relativePath.Substring(3);
    }
    return Path.Combine(dir.FullName, relativePath);
}