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.

Example 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
Example Output: B

Example Input: A timber company is dividing a 10,000 hectare forest into 5 sections. Which unit is most appropriate to use when showing the area of the divided sections?  
 (A) square inches (in.^2) (B) square meters (m^2) (C) square kilometers (km^2) (D) square centimeters (cm^2)
Example Output: C

Example Input: An astronomer observes that a planet rotates faster after a meteorite impact. Which is the most likely effect of this increase in rotation?  
 (A) Planetary density will decrease. (B) Planetary years will become longer. (C) Planetary days will become shorter. (D) Planetary gravity will become stronger.
Example Output:
C