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.

Example Input: A young ocean animal has two parents. Each of the parents has eight arms. How many arms does the young animal most likely have?  
 (A) 2 (B) 4 (C) 8 (D) 16
Example Output: C

Example Input: A research study concluded that people who work longer hours increase their chances of having higher blood pressure. This conclusion was developed from a study of 200 men of different ages. How is this investigation biased?  
 (A) The sample size was too large. (B) Scientists did not run the study. (C) Women were excluded from the study. (D) No medication was given to the men.
Example Output: C

Example Input: Which of the following structures is not present in animal cells?  
 (A) cell membrane (B) cell wall (C) mitochondrion (D) nucleus
Example Output:
B