instruction:
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.
question:
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
answer:
D


question:
Which two life processes occur in both plants and humans?  
 (A) growing and reproducing (B) germinating and making food (C) growing and making food (D) germinating and reproducing
answer:
A


question:
Which system is most responsible for transporting blood throughout the body?  
 (A) skeletal system (B) excretory system (C) digestive system (D) circulatory system
answer:

D