the mass unit troy ounce is used in what measurement system?
Entity
m.016sjv
Troy weight
class entity
measurement_unit.measurement_system m.02xk087
measurement_unit.measurement_system measurement_unit.mass_unit
Measurement System Troy ounce
none none
measurement_unit.measurement_system.weight_units
Mass Units
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> PREFIX : <http://rdf.freebase.com/ns/> 
SELECT (?x0 AS ?value) WHERE {
SELECT DISTINCT ?x0  WHERE { 
?x0 :type.object.type :measurement_unit.measurement_system . 
VALUES ?x1 { :m.02xk087 } 
?x0 :measurement_unit.measurement_system.weight_units ?x1 . 
FILTER ( ?x0 != ?x1  )
}
}
(AND measurement_unit.measurement_system (JOIN measurement_unit.measurement_system.weight_units m.02xk087))