AsyncObservables.SearchEngine.SearchEngineB.SearchAsync C# (CSharp) Method

        public async Task<IEnumerable<string>> SearchAsync(string term)
        {
            Console.WriteLine("SearchEngine B - SearchAsync()");
            await Task.Delay(1500);//simulate latency
            return new[] { "resultC", "resultD" }.AsEnumerable();
        }
    }

 public static IObservable<string> Search_DefferedConcatingTasks(string term)
 {
     var searchEngineA = new SearchEngineA();
     var searchEngineB = new SearchEngineB();
     var resultsA = Observable.Defer(() => searchEngineA.SearchAsync(term).ToObservable());
     var resultsB = Observable.Defer(() => searchEngineB.SearchAsync(term).ToObservable());
     return resultsA
         .Concat(resultsB)
         .SelectMany(x => x);
 }