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: Which substance is a compound?  
 (A) butter (B) nitrogen (C) hydrogen (D) ammonia
Example Output: D

Example Input: A student is trying to identify a mineral that has a nonmetallic luster and is black. It can also be scratched with a fingernail. According to the mineral reference sheet, the unidentified mineral is most likely  
 (A) mica. (B) magnetite. (C) hornblende. (D) quartz.
Example Output: A

Example Input: Which of the following is an acquired human characteristic?  
 (A) Eye color (B) Hair color (C) Height (D) Verbal accent
Example Output:
D