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.

[EX Q]: A student placed a small chip of limestone into a hydrochloric acid solution, and carbon dioxide gas was released. The carbon dioxide provided evidence that   
 (A) only a physical change occurred. (B) a chemical change occurred. (C) only a loss of mass occurred. (D) the formation of an element occurred.
[EX A]: B

[EX Q]: On a field trip, a student holds a frog and reports that it has slippery skin. This is an example of  
 (A) a measurement (B) a prediction (C) an explanation (D) an observation
[EX A]: D

[EX Q]: What happens to the chemical energy in methane's bonds when methane reacts with oxygen and forms H_{2}O and CO_{2}?  
 (A) It is released as heat. (B) It generates a current. (C) It increases product mass. (D) It is transformed into neutrons.
[EX A]:
A