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

[EX Q]: Which series correctly represents the levels of organization in an organism?  
 (A) cells -> organs -> organ system -> tissue (B) cells -> tissue -> organs -> organ system (C) tissue -> cells -> organ system -> organs (D) tissue -> organ system -> cells -> organs
[EX A]: B

[EX Q]: A medium-sized star in the middle of its life cycle, such as the Sun, is most likely to emit which color of light?  
 (A) red (B) blue (C) white (D) yellow
[EX A]:
D