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]: Which of the following correctly lists the organizational hierarchy of organisms from simplest to most complex?  
 (A) cells, organs, tissues, organ systems, organisms (B) cells, tissues, organs, organ systems, organisms (C) tissues, cells, organs, organ systems, organisms (D) tissues, organs, cells, organ systems, organisms
[EX A]: B

[EX Q]: When a tree suffers from a decreased ability to transport materials within the phloem, what is directly impacted?  
 (A) volume of water in the xylem (B) flow of necessary nutrients (C) response to environmental factors (D) rate of photosynthesis in leaves
[EX A]: B

[EX Q]: Which is the best explanation of the term ecology?  
 (A) the study of the nonliving parts of the environment (B) the study of the living parts of the environment (C) the study of the protection and renewal of natural resources (D) the study of organisms and their interactions with the environment
[EX A]:
D