sentences: an comets is a mean of mankind
docs: comets has solid_nucleus halley's_comet is planet. comets has ice comet is extraterrestrial_object. short_period_comet is periodic_comet. comet is subplanetary_stellar_orbiter. comet is astronomical_object. long_period_comet is periodic_comet. comets is like_dirty_snowballs. periodic_comet is comet.