sentences: the asteroid belt contains the largest concentration of asteroids in the solar system
docs: main_asteroid_belt is asteroid_belt. kuiper_belt_object is asteroid. asteroid is asteroid. asteroid is rocky_planetary_body. asteroids is big_rocks_adrift_in_space. asteroid is celestial_body. apollo_asteroids is earth_crossing_asteroids. asteroid_ceres is larger_than_many_moons. asteroid_belt is belt. asteroid is subplanetary_stellar_orbiter.