You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Input: Consider Input: In 2014, a break in a storm water pipe released thousands of gallons of coal ash from a retired electrical plant into a river. The spill occurred upstream from the water treatment plants that serve communities along the river. Coal ash contains several hazardous metals including arsenic. Which stage of the water treatment process is most likely to remove hazardous metals from the water?  
 (A) aeration (B) coagulation (C) disinfection (D) reverse osmosis

Output: B


Input: Consider Input: Which source of data about Nevada resources is likely to be most current and reliable?  
 (A) a science encyclopedia (B) an article in a local newspaper (C) a government-maintained website (D) a student's classroom presentation

Output: C


Input: Consider Input: Which of these factors affects how fast a sound wave moves?  
 (A) the kind of material it is moving through (B) the amplitude of the sound wave's vibrations (C) the wavelength of the disturbance in the medium (D) the type of motion that caused the sound wave to form


Output: A