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]: The floating arrow on a compass always points towards the  
 (A) west. (B) east. (C) south. (D) north.
[EX A]: D

[EX Q]: When microorganisms deplete the oxygen in soil through respiration, the soil becomes  
 (A) humus. (B) anaerobic. (C) compost. (D) aerobic.
[EX A]: B

[EX Q]: An Italian scientist named Alessandro Volta invented the Voltaic pile in 1800. It was able to produce a steady electrical current. Based on this description, what is the modern equivalent of the Voltaic pile?  
 (A) a wire (B) a battery (C) a resistor (D) a light bulb
[EX A]:
B