What is {material used} of {Tower Bridge} that is {applies to part} is {structural system} ?
The Tower Bridge is constructed of what material?
What material is the Tower Bridge made of?
SELECT ?a WHERE { ?o property:made_from_material ?a . ?o property:applies_to_part resource:structural_system . resource:Tower_Bridge property:made_from_material ?o }
select distinct ?obj  where {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <http://wikidata.dbpedia.org/resource/Q83125> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P186> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> ?obj .
?statement <http://www.wikidata.org/entity/P518> <http://wikidata.dbpedia.org/resource/Q2448108>
} 

SELECT ?obj WHERE { wd:Q83125 p:P186 ?s . ?s ps:P186 ?obj . ?s pq:P518 wd:Q2448108 }