Question: Who are the parents of the speaker at March on Washington for Jobs and Freedom?
Answer(s):
answer: Alberta Williams King
answer: Martin Luther King, Sr.

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:event.public_speaker.speeches_or_presentations ?k .
?k ns:event.speech_or_presentation.event ns:m.01lt0z . 
?c ns:people.person.parents ?x .
}