You are given a science question (hard-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.

Input: Consider Input: Which of these is never found in prokaryotic cells?  
 (A) cell membrane (B) ribosome (C) cell wall (D) nucleus

Output: D


Input: Consider Input: The respiratory system cannot deliver oxygen to the cells of the body, nor can it remove carbon dioxide, without which two body systems?  
 (A) muscular and nervous (B) digestive and muscular (C) cardiovascular and nervous (D) cardiovascular and muscular

Output: D


Input: Consider Input: Why does a plastic rod have a negative charge after being rubbed with a piece of fur?  
 (A) The fur gives up protons to the rod. (B) The rod gives up electrons to the air. (C) The fur gains protons from the rod. (D) The rod gains electrons from the fur.


Output: D