Simple categories matching challenging:

• location,
• occupation,
• activity,
• endeavor,
• works,
• discipline,
• surface,
• behavior,
• work,
• topic,
• thing,
• structure,
• environment,
• area,
• content,
• site,
• toy,
• industry,
• pursuit,
• space,
• application,
• situation,
• place,
• sport,
• movement,
• issue,
• task,
• illness,
• exercise,
• behaviour,
• event,
• game,
• sector,
• condition,
• project,
• domain,
• system,

Members with property challenging:

• word_bingo,
• camping,
• arthritis,
• scrabble,
• aggression,
• domestic_abuse,
• test,
• hilly_terrain,
• surface_alloy,
• shoulder,
• bicycling,
• traffic_corridor,
• swimming,
• migration,
• park,
• backpacking,
• agriculture,
• enterprise_architecture,
• neck,
• velocity_inversion,
• roadway,
• tunnel,
• coursework_content,
• chess,
• pitch,
• business,
• data_analysis,
• work_stress,
• archery,
• severity,
• presence,
• cooperative_game,
• urban_center,
• major_incident,
• canter_pirouette,
• chronic_pain,
• tactics_pin,
• asthma,
• calculus,
• subterranean_area,
• sport,
• cat_figure,
• piaffe_trot,
• accident,
• royalty_research,
• sculptural_mask,
• singing,
• music_therapy,
• hands,
• doctoral_study,
• land_law,
• wilderness_survival,
• divorce,
• game,
• soil_condition,
• plywood,
• cancer,
• dominoes,
• woodworking,
• boat,
• design,
• defiance,
• patio,
• playing_game,
• values,
• close_order,
• infection,
• head,
• asphalt,
• music,
• narrow_street,
• role_play,
• inadequate_planning,
• assault,
• intelligent_discussion,
• byte_bit,
• yoga,
• fixation,
• flood,
• military_confidence,
• memory_game,
• illiteracy,
• strain,
• oil_resistance,
• kick,
• archery_snooker,
• environmental_stress,
• squat,
• office,
• analysis,
• stress,
• house_building,
• flu,
• ethical_issue,
• waste,
• science,
• hypoxia,
• yeast,
• monopoly,
• invasive_species,
• building,
• cheddar_challenge,
• trek,
• statistics,
• race_relations,
• independent_research,
• diabetes,
• large_complex,
• standard,
• quiz,
• humour,
• pit,
• computational_biology,
• temper,
• security,
• astronomy,
• sleep_issue,
• hobby,
• lcd_interface,
• war,
• emergency_service,
• finance,
• circular_motion,
• frequent_disconnection,
• intimidation,
• construction,
• talent_show,
• smaller_area,
• parkway,
• engineering,
• physical_intervention,
• marine_biology,
• rotator-cuff_disease,
• epilepsy,
• ceiling,
• dancing,
• aggressive_behavior,
• modality,
• ecological_issue,
• crossword,
• technology,
• complex,
• biotech_lab,
• inner_thigh,
• cerebral_palsy,
• dance,
• driveway,
• remote_area,
• politics,
• extreme_heat,
• township_south,
• literature,
• crack,
• lip,
• climate_variation,
• london_marathon,
• new_technology,
• rooftop_garden,
• poker,
• thick_carpet,
• impulsiveness,
• office_automation,
• aerobics,
• aggressiveness,
• indoor_scene,
• thigh,
• treadmill,
• chin,
• laser_tag,
• tennis,
• philosophy,
• cricket,
• marathon,
• restraint,
• heat,
• archery_golf,
• gymnastics,
• multiple_sclerosis,
• penis,
• patient_motion,
• geology,
• helix_bundle,
• aviation,
• debate,
• curb,
• jubilee_bridge,
• tragedy,
• surfing,
• ecology,
• mummy_bowling,
• pool_deck,
• survival,
• systemic_sclerosis,
• checkers,
• intersection,
• ethics,
• south,
• restorative_practice,
• chronic_illness,
• apathy,
• reproduction,
• deforestation_pattern,
• over_rooftop,
• suicidal_behavior,
• prism,
• multipurpose_stadium,
• cathedral_ceiling,
• aqua_karate,
• cooking,
• right,
• skateboarding,
• horrific_accident,
• football,
• zero_visibility,
• approach,
• deep_squatting,
• fatality_accident,
• due_diligence,
• office_workspace,
• humidity,
• verbal_aggression,
• playing_chess,
• freestanding_facility,
• organization,
• bullying,
• cold,
• hopscotch,
• long_days,
• atrium,
• large_boardroom,
• use,
• poverty,
• research,
• wrestling,
• fly,
• pool,
• canyon_site,
• extreme_sport,
• skin_irritation,
• spoon_race,
• sailing,
• electric_power,
• campus,
• desert_condition,
• raft_building,
• molecular_beam,
• housework,
• ceramics,
• meteorology,
• pain,
• mountaineering,
• mental_grammar,
• hospitality_management,
• sheet,
• modern_dance,
• motion,
• uneven_dock,
• anemia,
• remote_village,
• wireless_setting,
• railway_tunnel,
• bright_light,
• leap,
• equine_therapy,
• current_fashion,
• rock-climbing_wall,
• christian_service,
• urban_core,
• frozen_terrain,
• tidal_stream,
• undulation,
• tourism,
• psychological_therapy,
• historical_building,
• muscular_dystrophy,
• ballet,
• spinal_trauma,
• marital_problem,
• trivial_pursuit,
• withdrawal,
• abuse,
• online_bingo,
• tag_rugby,
• turbid_condition,
• sporting_game,
• theatre,
• spine,
• outdoor_adventure,
• global_issue,
• personal_illness,
• interracial_dynamics,
• impact,
• winter_storm,
• discussion,
• bullfighting,
• finger,
• home,
• face,
• mind_bender,
• attack,
• multiculturalism,
• queer_theory,
• downhill_skiing,
• rock,
• art_project,
• toxic_waste,
• fatigue,
• missile_seeker,
• playing_bridge,
• tight_radius,
• detection,
• color,
• rooftop,
• biotechnology,
• material,
• order,
• severe_withdrawal,
• program_design,
• office_work,
• extreme_climate,
• anger,
• presbyopia,
• service,
• ear,
• mining_camp,
• letter_recognition,
• reading,
• number_work,
• strong_language,
• threat,
• snorkeling,
• acquisition,
• alzheimers,
• minimum_light,
• isolation,
• painting,
• discovery,
• curved_pillar,
• landscape,
• candy-cane_pull,
• kitchen,
• sidewalk,
• escarpment,
• play,
• network_analysis,
• intelligence,
• world_peace,
• class_disruption,
• snowboard_trip,
• biology,
• pushup,
• water_sculling,
• meditation,
• organized_sport,
• stereotype,
• olympic_game,
• concrete,
• cultural_understanding,
• basement_workroom,
• sexual_portrayal,
• outside_corner,
• service_quality,
• team_building,
• organ,
• separation,
• anxiety,
• craps,
• intense_aggression,
• social_problem,
• team_issue,
• earth_geometry,
• active_game,
• baseball,
• elephant_training,
• parcheesi,
• high_dome,
• contest,
• dementia,
• irritability,
• puzzling_plank,
• first_aid,
• self_injury,
• math,
• neuroscience,
• mammalian_cell,
• rope_course,
• tree_bark,
• proof_exercise,
• pool_bombing,
• counting_practice,
• passive_resistance,
• railing,
• maximal_use,
• drug_use,
• repetition,
• merger,
• allergy,
• terrace,
• eyes,
• social_issue,
• harassment,
• forward_planning,
• bridge,
• top,
• arab_world,
• relationship,
• grid_architecture,
• steps,
• team_course,
• speleology,
• measurement,
• paintball,
• violence,
• heel,
• dirt,
• transportation,
• decision,
• neglect,
• bathroom,
• intervention_service,
• cns,
• uneven_pavement,
• ceramic_tile,
• bankruptcy,
• doorsill,
• hospitalization,
• adaptive_property,
• tie,
• suicide,
• nim,
• financial_sophistication,
• arms,
• dim_lighting,
• land_use,
• development,
• democracy,
• waste_strategy,
• knowledge_representation,
• light_bar,
• fog,
• history,
• disrespect,
• backgammon,
• analogue_input,
• flats,
• failure_analysis,
• jowl,
• asian_crisis,
• religion,
• restlessness,
• dark,
• quality_assurance,
• dna_evidence,
• gardening,
• energy,
• foot,
• rope,
• construction_set,
• bush_fire,
• peer_interaction,
• tidal_flow,
• socratic_seminar,
• vibration,
• concert,
• wheelchair_basketball,
• law,
• stubbornness,
• audit,
• arts,
• radio,
• tissue,
• heavy_industry,
• fork,
• palate_deformity,
• wilderness,
• china,
• community_work,
• severe_aggression,
• murder,
• drama_workshop,
• golf,
• gm_technology,
• mental_aerobics,
• obstacle_course,
• nose,
• fissure,
• skiing,
• soil_painting,
• television_production,
• garage_ceiling,
• wine_blending,
• physical_aggression,
• stairway,
• trust_building,
• nuclear_waste,