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]: What are produced in both the male and female reproductive systems in humans?  
 (A) sperm (B) nutrients (C) fertilized eggs (D) sex cells
[A]: D


[Q]: 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
[A]: C


[Q]: When hunting by humans causes a species to become extinct, this may produce damaging effects throughout the ecosystem of the extinct species. What is the cause of this damage?  
 (A) alteration of a food web (B) degradation of a habitat (C) modification of a climate (D) reversal of a flow of energy
[A]:
A