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 organ is made mostly of muscle?  
 (A) heart (B) lung (C) ear (D) brain

A: A
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Q: A cut to the skin is treated with antiseptic first to avoid  
 (A) an immune response. (B) a bacterial infection. (C) bruising of tissues. (D) an allergic reaction.

A: B
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Q: Which structure controls what enters both plant cells and animal cells?  
 (A) nucleus (B) cell wall (C) chloroplast (D) cell membrane

A:
D
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