This question asks for the reason given in the passage for a characteristic feature of meteor streams. According to the passage, the dust particles in a meteor stream eventually surround a comet’s original orbit because of the different velocities at which they are ejected, as stated in choice A, the best answer. Choice B is directly contradicted by information in the passage. The other answer choices are incorrect because the passage does not say that the dust particles become part of the meteor stream at different times, or that their velocity slows over time.