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: what kind unit of length is associated with a measurement system whose mass units include atomic mass unit? 
Knowledge Triplets: Mass, base.ontologies.ontology_instance.equivalent_instances, m.07nfbgl
Tonne, measurement_unit.mass_unit.measurement_system, Non-SI units mentioned in the SI
atomic mass unit.noun.01, base.wordnet.synset.hypernym, mass unit.noun.01
Molecular mass, type.property.schema, Infobox_mineral
m.04kdl2t, dataworld.gardening_hint.replaced_by, Atomic mass unit
Mass, measurement_unit.dimension.units, Earth mass
Molecular mass, type.property.unit, Atomic mass unit
m.07s1l_7, base.wordnet.word_sense.sense, atomic mass unit.noun.01
Non-SI units mentioned in the SI, measurement_unit.measurement_system.length_units, Astronomical unit
m.019h, type.permission.controls, m.0qn08p5
Second of arc, measurement_unit.angle_unit.measurement_system, Non-SI units mentioned in the SI
Non-SI units mentioned in the SI, measurement_unit.measurement_system.time_units, Day
Megaelectronvolt, measurement_unit.energy_unit.measurement_system, Non-SI units mentioned in the SI
Atomic mass, type.type.properties, Mass
Molecular mass, type.property.unique, true
Atomic mass unit, user.benvvalk.default_domain.moby_output_descriptor.uri, http://ncicb.nci.nih.gov/xml/owl/EVS/Thesaurus.owl#Atomic_Mass_Unit
Infobox_mineral, type.type.properties, Molecular mass
Mass, measurement_unit.dimension.units, Picul
m.07vn7ph, base.yupgrade.user.topics, Mass
mass.noun.01, base.wordnet.synset.equivalent_topic, Mass
Mass, measurement_unit.dimension.units, Long quarter
Mass, measurement_unit.dimension.units, Troy ounce
Mass, measurement_unit.dimension.units, Gram
Mass, measurement_unit.dimension.units, Milligram
Mass, measurement_unit.dimension.units, Short quarter
Mass, measurement_unit.dimension.units, Solar mass
Molecular mass, type.property.expected_type, Floating Point Number
Mass, type.property.unit, Atomic mass unit
m.0tfn3w7, dataworld.gardening_hint.last_referenced_by, m.0qn08p5
Electronvolt, measurement_unit.energy_unit.measurement_system, Non-SI units mentioned in the SI
m.0123pbz6, base.fbontology.predicate_path.properties, Mass
Minute of arc, measurement_unit.angle_unit.measurement_system, Non-SI units mentioned in the SI
Mass, measurement_unit.dimension.units, Planck mass
Non-SI units mentioned in the SI, measurement_unit.measurement_system.energy_units, Electronvolt
atomic mass unit.noun.01, base.wordnet.synset.lexname, noun.quantity
g.125_nqqmb, base.schemastaging.pronunciation.yomigana, とういつげんししつりょうたんい
Day, measurement_unit.time_unit.measurement_system, Non-SI units mentioned in the SI
Hour, measurement_unit.time_unit.measurement_system, Non-SI units mentioned in the SI
Uncertainty, type.property.unique, true
atomic mass unit.noun.01, base.wordnet.synset.syntactic_category, Noun
Mass, measurement_unit.dimension.units, Pound
Minute, measurement_unit.time_unit.measurement_system, Non-SI units mentioned in the SI
Mass, base.schemastaging.context_name.pronunciation, g.125_l6gm1
Mass, base.skosbase.vocabulary_equivalent_topic.equivalent_concept, Mass (Physics)
Non-SI units mentioned in the SI, base.schemastaging.context_name.pronunciation, g.125_q35jr
Non-SI units mentioned in the SI, measurement_unit.measurement_system.angle_units, Second of arc
Uncertainty, type.property.schema, Atomic mass
Uncertainty, type.property.expected_type, Floating Point Number
m.07nfbgl, base.ontologies.ontology_instance_mapping.freebase_topic, Mass
Mass, measurement_unit.dimension.units, Ounce
Mass, measurement_unit.dimension.units, Troy pound
mass unit.noun.01, base.wordnet.synset.hyponymy, atomic mass unit.noun.01
Mass (Physics), base.skosbase.skos_concept.equivalent_topic, Mass
Non-SI units mentioned in the SI, measurement_unit.measurement_system.weight_units, Tonne
Mass, measurement_unit.dimension.units, Candareen
Mass, measurement_unit.dimension.units, Kilogram
Mass, measurement_unit.dimension.units, Planetary mass
Millibar, measurement_unit.pressure_unit.measurement_system, Non-SI units mentioned in the SI
m.025d6_q, type.permission.controls, Uncertainty
m.025d6_q, type.permission.controls, Mass
Non-SI units mentioned in the SI, measurement_unit.measurement_system.energy_units, Megaelectronvolt
m.0qn08p5, type.object.permission, m.019h
Mass, type.property.schema, Atomic mass
atomic mass unit.noun.01, base.wordnet.synset.word, m.07s1l_7
Non-SI units mentioned in the SI, measurement_unit.measurement_system.angle_units, Minute of arc
Mass, measurement_unit.dimension.units, Jupiter mass
Mass, measurement_unit.dimension.units, Dram
Ana Marie Cox, base.yupgrade.user.topics, Mass
Mass, measurement_unit.dimension.units, Cash
Degree, measurement_unit.angle_unit.measurement_system, Non-SI units mentioned in the SI
Non-SI units mentioned in the SI, measurement_unit.measurement_system.angle_units, Degree
Non-SI units mentioned in the SI, measurement_unit.measurement_system.volume_units, Liter
atomic mass unit.noun.01, base.wordnet.synset.equivalent_topic, Atomic mass unit
Mass, measurement_unit.dimension.units, Electron rest mass
Non-SI units mentioned in the SI, measurement_unit.measurement_system.angle_units, Angular mil
Mass, measurement_unit.dimension.units, Short ton
Molecular mass, type.object.permission, m.075xzy_
Atomic mass unit, measurement_unit.mass_unit.measurement_system, Non-SI units mentioned in the SI
Mass, measurement_unit.dimension.units, Catty
Angular mil, measurement_unit.angle_unit.measurement_system, Non-SI units mentioned in the SI
Uncertainty, type.property.unit, Atomic mass unit
Uncertainty, type.object.permission, m.025d6_q
Hectare, measurement_unit.area_unit.measurement_system, Non-SI units mentioned in the SI
Mass, type.object.permission, m.025d6_q
Non-SI units mentioned in the SI, measurement_unit.measurement_system.area_units, Hectare
Floating Point Number, type.type.expected_by, Molecular mass
Mass, measurement_unit.dimension.units, Stone
Mass, measurement_unit.dimension.units, Pennyweight
Non-SI units mentioned in the SI, measurement_unit.measurement_system.solid_angle_units, Square degree
Non-SI units mentioned in the SI, measurement_unit.measurement_system.weight_units, Atomic mass unit
Mass, type.property.expected_type, Floating Point Number
Mass, user.avh.default_domain.ellerdale_topic.ellerdale_id, 0080-0198
m.075xzy_, type.permission.controls, Molecular mass
m.0qn08p5, dataworld.gardening_hint.last_referenced_by, Atomic mass unit
Floating Point Number, type.type.expected_by, Uncertainty
Wired, base.yupgrade.user.topics, Mass
Atomic mass unit, measurement_unit.mass_unit.weightmass_in_kilograms, 1.660538782e-27
m.075_7gq, base.yupgrade.user.topics, Mass
m.0123pbzp, base.fbontology.predicate_path.prop_2, Mass
Mass, measurement_unit.dimension.units, Microgram
Mass, measurement_unit.dimension.units, Tael
Atomic mass, type.type.properties, Uncertainty
Non-SI units mentioned in the SI, measurement_unit.measurement_system.pressure_units, Millibar
Liter, measurement_unit.volume_unit.measurement_system, Non-SI units mentioned in the SI
noun.quantity, base.wordnet.lexical_name.synsets, atomic mass unit.noun.01
Mass, measurement_unit.dimension.units, Mace
Atomic mass unit, base.schemastaging.context_name.pronunciation, g.125_nqqmb
atomic mass unit.noun.01, base.wordnet.synset.gloss, unit of mass for expressing masses of atoms or molecules
Mass, measurement_unit.dimension.units, Cental
Mass, measurement_unit.dimension.units, Long ton
Floating Point Number, type.type.expected_by, Mass
m.0123pbz6, base.fbontology.predicate_path.prop_2, Mass
Mass, measurement_unit.dimension.units, Carat
Mass, type.property.unique, true
Mass, measurement_unit.dimension.units, Hundredweight
Mass, measurement_unit.dimension.si_base_unit, Kilogram
Bar, measurement_unit.pressure_unit.measurement_system, Non-SI units mentioned in the SI
Mass, measurement_unit.dimension.units, Atomic mass unit
Mass, measurement_unit.dimension.units, MeV/c²
m.0qplrls, dataworld.gardening_hint.last_referenced_by, Mass
Non-SI units mentioned in the SI, measurement_unit.measurement_system.time_units, Hour
m.0123pbzp, base.fbontology.predicate_path.properties, Mass
Mass, measurement_unit.dimension.units, Tonne
Non-SI units mentioned in the SI, measurement_unit.measurement_system.pressure_units, Bar
Square degree, measurement_unit.solid_angle_unit.measurement_system, Non-SI units mentioned in the SI
Astronomical unit, measurement_unit.distance_unit.measurement_system, Non-SI units mentioned in the SI
Non-SI units mentioned in the SI, measurement_unit.measurement_system.time_units, Minute
Mass, measurement_unit.dimension.units, Grain

Answer: Astronomical unit