Question: Who is Serena Williams sports team quarterback?
Answer(s):
answer: Matt Moore
answer: Ryan Tannehill

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:sports.professional_sports_team.owner_s ns:m.015z4j . 
?c ns:sports.sports_team.roster ?y .
?y ns:sports.sports_team_roster.player ?x .
?y ns:sports.sports_team_roster.position ns:m.06b1q .
FILTER(NOT EXISTS {?y ns:sports.sports_team_roster.from ?sk0} || 
EXISTS {?y ns:sports.sports_team_roster.from ?sk1 . 
FILTER(xsd:datetime(?sk1) <= "2015-08-10"^^xsd:dateTime) })
FILTER(NOT EXISTS {?y ns:sports.sports_team_roster.to ?sk2} || 
EXISTS {?y ns:sports.sports_team_roster.to ?sk3 . 
FILTER(xsd:datetime(?sk3) >= "2015-08-10"^^xsd:dateTime) })
}