Definition: In this task, you are given a multiple-choice question and you have to pick the correct option. Answer with option indexes (i.e., "A", "B", "C", and "D").
Input: What covers over 90% of the Earth's surface and 0% of the moon's surface (A) a magnesium iron silicate mineral (B) chemical element with the symbol S (C) the element with the symbol Fe (D) that which contains 2 hydrogen and 1 oxygen molecules
Output:
D