The sentence in question (21) reads: "They were changed into a frost giant whose name was Ymir (e’mir)." The subject "they" refers to the ice mountains that melted, suggesting a transformation rather than a chronological sequence or an adversative relationship.
Among the options given, the best choice that maintains the meaning of the original sentence while improving clarity is:
B: "There they were changed into a frost giant whose name was Ymir (e’mir)."
This option clarifies location and context more effectively without introducing unnecessary temporal or adversative elements.
So, the answer is B.