link中用string.cocat为什么得到的结果输出不了？

Console.WriteLine("aaa".Concat("bbb"));
'string.Concat(params string[])' cannot be accessed with an instance reference;

 Console.WriteLine(new string("aaa".AsEnumerable<char>().Concat("bbb").ToArray()));

http://stackoverflow.com/questions/1100009/member-method-cannot-be-accessed-with-an-instance-reference