Question: Which other political offices, has the public speaker which spoke about energy development, worked as?
Answer(s):
answer: United States Senator
answer: Illinois State Senator

SPARQL query:
#MANUAL SPARQL
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
  FILTER (?x != ?c)
?c ns:event.public_speaker.speeches_or_presentations ?k .
?k ns:event.speech_or_presentation.speech_topic ns:m.02mg6f . 
?c ns:government.politician.government_positions_held ?y .
  ?y ns:government.government_position_held.office_position_or_title ?x ;
     ns:government.government_position_held.to ?d .  # the position has ended; not the current position
}