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]: When do mutations help make an ecosystem more sustainable?  
 (A) when mutations decrease the number of individuals in an ecosystem (B) when mutations increase the number of individuals in an ecosystem (C) when mutations decrease the number of species in an ecosystem (D) when mutations increase the number of species in an ecosystem
[EX A]: D

[EX Q]: A boy pulls a sweater off over his head. His hair is attracted to the sweater due to  
 (A) a magnetic force (B) a heat transfer (C) a chemical change (D) an electrical charge
[EX A]: D

[EX Q]: Which tool is best used to observe a soil sample?  
 (A) camera (B) compass (C) hand lens (D) telescope
[EX A]:
C