Final answer:
Comet nuclei could have brought refractory and volatile elements to terrestrial planets, contributed to the formation of the Moon, but did not remove the atmosphere of Mercury.
Step-by-step explanation:
Comet nuclei, which are composed of volatiles and solids, could have been responsible for bringing both refractory and volatile elements to terrestrial planets. As these comets bombarded the inner planets, they delivered ice-rich material that had condensed in the outer part of the solar nebula.
This ice-rich material contained elements that were critical to the formation of life, such as water and organic compounds. Therefore, option A and option B are both correct.
Furthermore, the impact of comets may have played a role in forming the Moon. It is believed that a giant impact between Earth and a Mars-sized object led to the ejection of material that later coalesced to form the Moon. So, option C is also correct.
However, there is no evidence to suggest that the showers of comet nuclei were responsible for removing the atmosphere of Mercury. So, option D is not correct.