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]: What gas in the air do we need to breathe in order to live?  
 (A) nitrogen (B) oxygen (C) carbon dioxide (D) hydrogen (E) water vapor
[EX A]: B

[EX Q]: Which of the following events during meiosis contributes most to the variation within a species?  
 (A) pairing of chromosomes (B) creation of haploid gametes (C) segregation of alleles (D) separation of chromatids
[EX A]:
C