Question: Where is the Chelsea Bridge River's source located?
Answer(s):
answer: Thames Head

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ?c)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
?c ns:geography.body_of_water.bridges ns:m.02vfg1 . 
?c ns:geography.river.origin ?x .
}