Name the most-produced rolling stock class operated by the New York City Subway ?
select ?ent where { ?ent wdt:P31 wd:Q811704 . ?ent wdt:P1092 ?obj . ?ent wdt:P137 wd:Q7733 } ORDER BY DESC(?obj)LIMIT 5 
rolling stock class: Q811704 new york city subway: Q7733