user: You are a structured reasoning expert tasked with solving problems step by step. 
You first think about the reasoning process in the mind and then provide the answer. The reasoning process and answer should be enclosed within <think> </think> and <answer> </answer> tags, respectively, i.e., <think> reasoning process here </think> <answer> answer here </answer>. 
Given a question and the associated knowledge graph triplets (entity, relation, entity), you are asked to answer the question with these triplets and your own knowledge. 
You can break down the original question into several sub-questions and explore the given knowledge graph to solve them step-by-step. If there are multiple possible answers, choose one as the final answer. 
After thinking, when you finally reach a conclusion, clearly state the answer within <answer> </answer> tags, i.e., <answer> answer here </answer>. 
Question: the mass unit troy ounce is used in what measurement system? 
Knowledge Triplets: Mass, measurement_unit.dimension.units, Tonne
Mass, measurement_unit.dimension.units, Electron rest mass
m.075_7gq, base.yupgrade.user.topics, Mass
Mass, measurement_unit.dimension.units, Grain
Mass, base.skosbase.vocabulary_equivalent_topic.equivalent_concept, Mass (Physics)
Mass, base.ontologies.ontology_instance.equivalent_instances, m.07nfbgl
Mass, measurement_unit.dimension.units, Hundredweight
Pennyweight, measurement_unit.mass_unit.measurement_system, Troy weight
m.0qplrls, dataworld.gardening_hint.last_referenced_by, Mass
m.07vn7ph, base.yupgrade.user.topics, Mass
Wired, base.yupgrade.user.topics, Mass
Troy ounce, measurement_unit.mass_unit.weightmass_in_kilograms, 0.0311034768
Mass, measurement_unit.dimension.units, Milligram
Mass, measurement_unit.dimension.units, Stone
Mass, measurement_unit.dimension.units, Troy ounce
Mass, measurement_unit.dimension.units, Mace
Mass, measurement_unit.dimension.units, Microgram
Troy ounce, measurement_unit.mass_unit.measurement_system, Troy weight
Mass, measurement_unit.dimension.units, Pound
Mass, measurement_unit.dimension.units, Atomic mass unit
Mass, measurement_unit.dimension.units, Cash
Troy weight, measurement_unit.measurement_system.weight_units, Troy pound
Mass, measurement_unit.dimension.units, Kilogram
Grain, measurement_unit.mass_unit.measurement_system, Troy weight
Mass, measurement_unit.dimension.units, Planck mass
Mass, measurement_unit.dimension.units, Long quarter
Mass, measurement_unit.dimension.units, Long ton
Troy weight, measurement_unit.measurement_system.weight_units, Pennyweight
Troy weight, measurement_unit.measurement_system.weight_units, Grain
Mass, measurement_unit.dimension.units, Earth mass
mass.noun.01, base.wordnet.synset.equivalent_topic, Mass
m.07nfbgl, base.ontologies.ontology_instance_mapping.freebase_topic, Mass
Mass, measurement_unit.dimension.units, Carat
Mass, measurement_unit.dimension.units, Gram
Mass, measurement_unit.dimension.si_base_unit, Kilogram
Troy weight, measurement_unit.measurement_system.weight_units, Troy ounce
Mass, measurement_unit.dimension.units, Picul
Troy ounce, measurement_unit.measurement_system.weight_units, Troy weight
Mass, measurement_unit.dimension.units, MeV/c²
Mass, measurement_unit.dimension.units, Ounce
Mass, measurement_unit.dimension.units, Dram
Troy pound, measurement_unit.mass_unit.measurement_system, Troy weight
troy.noun.01, base.wordnet.synset.equivalent_topic, Troy weight
Mass, measurement_unit.dimension.units, Pennyweight
Mass (Physics), base.skosbase.skos_concept.equivalent_topic, Mass
Mass, measurement_unit.dimension.units, Catty
Troy weight, symbols.namesake.named_after, Troyes
Mass, measurement_unit.dimension.units, Candareen
Mass, measurement_unit.dimension.units, Cental
Troyes, symbols.name_source.namesakes, Troy weight
Mass, user.avh.default_domain.ellerdale_topic.ellerdale_id, 0080-0198
Mass, measurement_unit.dimension.units, Troy pound
Mass, measurement_unit.dimension.units, Tael
Mass, base.schemastaging.context_name.pronunciation, g.125_l6gm1
Mass, measurement_unit.dimension.units, Solar mass
Ana Marie Cox, base.yupgrade.user.topics, Mass
Mass, measurement_unit.dimension.units, Short ton
Mass, measurement_unit.dimension.units, Planetary mass
Mass, measurement_unit.dimension.units, Jupiter mass
Mass, measurement_unit.dimension.units, Short quarter

Answer: Troy weight