Question: Who was the US President at the time when the Anti-Apartheid speaker was killed?
Answer(s):
answer: Lyndon B. Johnson

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.speech_topic ns:m.04lxyz0 . 
?c ns:government.us_president.vice_president ?x .
}