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: Some bacteria use iron found in their systems as a means to guide their movement. Which stimulus most likely triggers this movement mechanism?  
 (A) magnetism (B) oxygen (C) light (D) heat

Output: A


Input: Consider Input: Which body system's primary function is the continuation of the species?  
 (A) digestive (B) nervous (C) excretory (D) reproductive

Output: D


Input: Consider Input: Which is most like the way a stem supports a flower?  
 (A) the way water supports a boat crossing a river (B) the way a flagpole supports a flag in the schoolyard (C) the way bookends support books on a shelf (D) the way a belt supports pants on a person's waist


Output: B