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]: Which of the following would be more likely to pollute a river?  
 (A) allowing beavers to build a dam (B) spreading fertilizer near the river (C) mowing the grass on the river bank (D) fishing from a bridge over the river
[A]: B


[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]: Maria collected the gas given off by a glowing piece of charcoal. The gas was then bubbled through a small amount of colorless limewater. Part of Maria's report stated, "After the gas was put into the jar, the limewater gradually changed to a milky white color." This statement is  
 (A) an observation (B) a conclusion (C) a generalization (D) an assumption of the investigation (E) a hypothesis
[A]:
A