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]: Oxygen reacts with iron to produce rust and with hydrogen to produce water. Which statement describes both reactions?  
 (A) A different mixture is formed in each case. (B) A different solution is formed in each case. (C) Both a change of state and of elements is involved. (D) New molecules are formed but the same elements exist.
[A]: D


[Q]: Which is a response of the autonomic nervous system that helps maintain equilibrium in the body?  
 (A) shivering in cold temperatures (B) eating due to appetite (C) slapping at biting insects (D) pulling away from hot objects
[A]: A


[Q]: Electron transport in mitochondria results in a chemiosmotic gradient of which particle across the mitochondrial membrane?  
 (A) ADP (B) ATP (C) protons (D) neutrons
[A]:
C