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.

[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
[A]: B


[Q]: Which of the following was most likely the cause of the extinction of 60-100 species of native birds in Hawaii since the arrival of colonists?  
 (A) habitat destruction (B) volcanic eruptions (C) increased salinity (D) tidal waves
[A]: A


[Q]: When animals use energy, what is always produced?  
 (A) sugar (B) heat (C) oxygen (D) starch
[A]:
B