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 Input:
The most significant human-induced impact on Earth's atmosphere comes from the use of which energy resource?  
 (A) flowing water (B) fossil fuels (C) sunlight (D) winds

Ex Output:
B


Ex Input:
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 Output:
D


Ex Input:
Arteries and veins are two important parts of the circulatory system. What is the relationship between arteries and veins?  
 (A) They work together to exchange gases. (B) They work together to transport nutrients. (C) They work independently to remove wastes. (D) They work independently to relay messages.

Ex Output:

B