Problem with query in dotNetRDF

my main function says--

static void Main(string[] args) {

        Graph g = new Graph();
        FileLoader.Load(g, "\\cbcs.owl");

        TripleStore store = new TripleStore();
        store.Add(g);
        //Object results = store.ExecuteQuery("SELECT * WHERE { { ?s ?p ?o } UNION { GRAPH ?g { ?s ?p ?o } } }");

        Object results = store.ExecuteQuery("PREFIX pre:<http://www.cbcs.com/ontologies/cbcs.owl#>" + "SELECT ?X ?Y WHERE { ?X pre:hasInstitutes ?Y .}");
        SparqlResultSet rset = (SparqlResultSet)results;

        //Enumerating via the Results property
        foreach (SparqlResult result in rset.Results)
        {
            Console.WriteLine(result.ToString());
        }

        Console.WriteLine("hello");
        Console.ReadLine();
    }

but it doesnt display the answer if my query is simple and without answer it works but with prefix it doesnt please help