直接在文本看代码，谁能指出错在哪里

using System;
using System.IO;
//using ddd;

namespace ddaaaaaaaa
{
    public class Test : ddd.ISomeThingFunction
    {
        public Test()
        {

        }

        public void Test1()
        {

        }

        public void haha()
        {
            throw new NotImplementedException();
        }
    }
    public class Test11
    {

        void ddd()
        {
            Test t = new Test();
            //t.NBFunction();
            t.NBFunction("");
        }
    }

}

namespace ddd
{
    public interface ISomeThingFunction
    {
        void haha();
    }
    public static class ExtendFunction
    {
        public static void NBFunction(this ISomeThingFunction dd,string str)
        {

        }
    }
}