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 substance do all living things require to survive?  
 (A) blood (B) water (C) carbon dioxide (D) organic soil

A: B
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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
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Q: A light bulb transforms electrical energy into light energy. A light bulb also transforms electrical energy into  
 (A) heat energy (B) potential energy (C) magnetic energy (D) mechanical energy

A:
A
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