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.
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Question: The ocean minimum zone, or OMZ, is an area from 200 to 600 meters below the ocean's surface. The OMZ is dark and cold, with oxygen concentrations less than 10% of concentrations in surface water. Oxygen concentrations are so low because of bacterial activity that breaks down organic material falling from surface waters. Given the conditions in the OMZ, which of these dissolved gases would you expect to find in large concentrations in this zone?
(A) argon (B) nitrogen (C) carbon dioxide (D) carbon monoxide

Answer: C

Question: What form of energy is being used when a person pushes a wooden block across the floor?
(A) mechanical (B) magnetic (C) sound (D) electrical

Answer: A

Question: Which body system is most affected by a disease that causes the bones to become weak and brittle?
(A) excretory (B) muscular (C) skeletal (D) nervous

Answer:
C