You are given a science question (easy-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.

[EX Q]: Which of these substances is correctly identified as a mineral?  
 (A) coal (B) quartz (C) granite (D) sandstone
[EX A]: B

[EX Q]: Which material best conducts heat and electricity?  
 (A) metal (B) plastic (C) rubber (D) wood
[EX A]: A

[EX Q]: Of the examples listed, which event is thought by scientists to have led to the greatest extinction?  
 (A) a volcano in Hawaii erupting (B) the construction of the Hoover Dam (C) whalers of the 17th, 18th, and 19th centuries (D) the Mississippi River flooding its banks each summer
[EX A]:
C