Question: What sports team has a home stadium called Estadio Nacional and signed Cristiano Ronaldo in 2010?
Answer(s):
answer: Portugal national football team

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ns:m.02xt6q)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
ns:m.02xt6q ns:sports.pro_athlete.teams ?y .
?y ns:sports.sports_team_roster.team ?x .
FILTER(NOT EXISTS {?y ns:sports.sports_team_roster.from ?sk0} || 
EXISTS {?y ns:sports.sports_team_roster.from ?sk1 . 
FILTER(xsd:datetime(?sk1) <= "2010-12-31"^^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) >= "2010-01-01"^^xsd:dateTime) })
?x ns:sports.sports_team.arena_stadium ns:m.05j4lt . 
}