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.
--------
Question: 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.

Answer: A


Question: How many elements are in the compound Mg(OH)2?   
 (A) 2 (B) 3 (C) 4 (D) 5

Answer: B


Question: Which describes a property of all elements?  
 (A) All elements are metals. (B) All elements have six electrons. (C) All elements are pure substances. (D) All elements exist in the solid phase.

Answer:
C