Final answer:
In Norse mythology, Ymir's skull was used by Odin and his brothers to create the sky, and not directly the Sun, the Moon, the Stars, or the Planets as given in the options.
Step-by-step explanation:
The subject of the student's question pertains to Norse mythology, specifically a detail from the Prose Edda. In Norse creation myths, the skull of the primeval giant Ymir was used by Odin and his brothers to create the heavens. However, the question seems to have a slight mix-up.
According to the Prose Edda, the answer to 'What came from Ymir's skull?' would be the sky itself, which is not mentioned in the options provided. The Sun, the Moon, the Stars, and the Planets are celestial bodies within the sky, but they are not directly created from Ymir's skull according to the myth.