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

SOLUTION: D

PROBLEM: When do mutations help make an ecosystem more sustainable?  
 (A) when mutations decrease the number of individuals in an ecosystem (B) when mutations increase the number of individuals in an ecosystem (C) when mutations decrease the number of species in an ecosystem (D) when mutations increase the number of species in an ecosystem

SOLUTION: D

PROBLEM: Grasses, shrubs, and trees are called producers because they make  
 (A) water (B) carbon dioxide (C) minerals (D) food

SOLUTION:
D