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: in which measurement system square degree is the solid angle unit? 
Knowledge Triplets: Day, measurement_unit.time_unit.measurement_system, Non-SI units mentioned in the SI
Square degree, measurement_unit.solid_angle_unit.angle_in_steradians, 0.000304617419787
Minute, measurement_unit.time_unit.measurement_system, Non-SI units mentioned in the SI
Non-SI units mentioned in the SI, measurement_unit.measurement_system.angle_units, Minute of arc
Solid angle, user.avh.default_domain.ellerdale_topic.ellerdale_id, 009a-52ae
Non-SI units mentioned in the SI, measurement_unit.measurement_system.angle_units, Angular mil
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.angle_units, Degree
Minute 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.energy_units, Megaelectronvolt
Non-SI units mentioned in the SI, measurement_unit.measurement_system.length_units, Astronomical unit
Atomic mass unit, measurement_unit.mass_unit.measurement_system, Non-SI units mentioned in the SI
Megaelectronvolt, measurement_unit.energy_unit.measurement_system, Non-SI units mentioned in the SI
Solid angle, measurement_unit.dimension.units, Square degree
Solid angle, measurement_unit.dimension.si_base_unit, Steradian
Non-SI units mentioned in the SI, measurement_unit.measurement_system.time_units, Day
Non-SI units mentioned in the SI, measurement_unit.measurement_system.solid_angle_units, Square degree
g.125_l0f8w, base.schemastaging.pronunciation.yomigana, へいほうど
Solid angle, measurement_unit.dimension.units, Steradian
Bar, measurement_unit.pressure_unit.measurement_system, Non-SI units mentioned in the SI
Non-SI units mentioned in the SI, measurement_unit.measurement_system.time_units, Hour
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.weight_units, Atomic mass unit
Square degree, measurement_unit.solid_angle_unit.measurement_system, Non-SI units mentioned in the SI
Square degree, base.schemastaging.context_name.pronunciation, g.125_l0f8w
Non-SI units mentioned in the SI, measurement_unit.measurement_system.energy_units, Electronvolt
Non-SI units mentioned in the SI, measurement_unit.measurement_system.weight_units, Tonne
Liter, measurement_unit.volume_unit.measurement_system, Non-SI units mentioned in the SI
Tonne, measurement_unit.mass_unit.measurement_system, Non-SI units mentioned in the SI
Non-SI units mentioned in the SI, measurement_unit.measurement_system.time_units, Minute
Non-SI units mentioned in the SI, measurement_unit.measurement_system.angle_units, Second of arc
Non-SI units mentioned in the SI, measurement_unit.measurement_system.pressure_units, Bar
Electronvolt, measurement_unit.energy_unit.measurement_system, Non-SI units mentioned in the SI
Millibar, measurement_unit.pressure_unit.measurement_system, Non-SI units mentioned in the SI
Angular mil, measurement_unit.angle_unit.measurement_system, Non-SI units mentioned in the SI
Hectare, measurement_unit.area_unit.measurement_system, Non-SI units mentioned in the SI
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.pressure_units, Millibar
Hour, measurement_unit.time_unit.measurement_system, Non-SI units mentioned in the SI
Non-SI units mentioned in the SI, measurement_unit.measurement_system.area_units, Hectare
Non-SI units mentioned in the SI, measurement_unit.measurement_system.volume_units, Liter
solid angle.noun.01, base.wordnet.synset.equivalent_topic, Solid angle
Non-SI units mentioned in the SI, base.schemastaging.context_name.pronunciation, g.125_q35jr
Solid angle, base.schemastaging.context_name.pronunciation, g.125_rt7t7

Answer: Non-SI units mentioned in the SI