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.

Example Input: Which illness is always caused by an infection?  
 (A) a heart attack (B) a broken bone (C) influenza (D) cancer
Example Output: C

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

Example Input: How are bacterial cells and human cells alike?  
 (A) They allow oxygen through the cell wall. (B) They allow carbon dioxide through the cell wall. (C) They allow nutrients through the cell membrane. (D) They allow nutrients through the nuclear membrane.
Example Output:
C