PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>  
PREFIX : <http://example.org/test#>

SELECT ?x
WHERE { 
   ?x a [
       a owl:Class ;
       owl:unionOf ( :B :C )
   ] . 
}
