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]: The Sun is classified as  
 (A) an organism (B) a decomposer (C) a star (D) a planet
[EX A]: C

[EX Q]: Planting certain crop plants in a field causes a disruption of the natural nitrogen cycle in that field. Which outcome would this disruption most DIRECTLY cause in the field over time?  
 (A) topsoil erodes (B) soil nutrients decrease (C) desert conditions appear (D) atmospheric carbon dioxide increases
[EX A]: B

[EX Q]: At science conventions, scientists present their research, and members of the audience can discuss or ask questions about the research. The main value of these science conventions is that they allow scientists to  
 (A) see new places. (B) find money for projects. (C) practice public speaking. (D) exchange their ideas.
[EX A]:
D