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]: Living things are classified as producers or consumers according to  
 (A) their speed of movement (B) the size of their communities (C) how they obtain food (D) how they reproduce
[A]: C


[Q]: Which substance do all living things require to survive?  
 (A) blood (B) water (C) carbon dioxide (D) organic soil
[A]: B


[Q]: What event is most likely responsible for a rapid change at the surface of Earth?  
 (A) an earthquake (B) a cold front (C) a continental glacier (D) a thunderstorm
[A]:
A