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 human organ system eliminates liquid and gaseous wastes from the body?  
 (A) circulatory (B) endocrine (C) excretory (D) reproductive
[A]: C


[Q]: All of the different organisms interacting in a pond make up  
 (A) a community (B) a population (C) the water cycle (D) the habitat
[A]: A


[Q]: Scientists estimate that Maryland contains more than 850 million tons of coal. Coal is most commonly used to produce ___.  
 (A) electricity (B) medicine (C) metals (D) water
[A]:
A