This question asks you to identify an accurate statement about meteor streams. Choice C, the best answer, restates information about the composition of meteor streams from the first sentence of the passage. Choice A is not correct. The passage discusses the influence of planetary gravitation on meteor streams but says nothing about its influence on the orbits of comets. According to the passage, it is planetary gravitation, not the gravitational fields of comets, that causes meteor streams to increase in size, so choice B is not correct. And choice D is not correct because the passage says nothing about the composition of comets.