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: The burning of fossil fuels affects the atmosphere by
(A) adding more heat and carbon dioxide. (B) reducing the amount of necessary heat. (C) taking water vapor out of the atmosphere. (D) putting more oxygen in the atmosphere.

Answer: A

Question: Research in which of these areas has the greatest impact on the environment?
(A) irradiating food (B) organic fertilizers (C) bacteria to clean up oil spills (D) developing larger, sweeter strawberries

Answer: C

Question: A unicellular organism is best described as being
(A) a complex organism. (B) a microorganism. (C) an organism with specialized cells. (D) an organism with different types of tissues.

Answer:
B