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]: All of the different organisms interacting in a pond make up  
 (A) a community (B) a population (C) the water cycle (D) the habitat
[A]: A


[Q]: Which type of organism is the best at fixing nitrogen?  
 (A) bacteria (B) fungi (C) protists (D) animals
[A]: A


[Q]: Clear cutting of old growth forests in Oregon provides lumber for housing. In the process of clear cutting, plant diversity decreases and some organisms are pushed to extinction. Clear cutting is an example of  
 (A) a change in aquatic conditions. (B) a change in societal conditions. (C) a change in atmospheric conditions. (D) a change in environmental conditions.
[A]:
D