Definition: 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: Which of the following does not affect the strength of an electromagnet?
(A) number of times the wire is looped around the core (B) size of the object being attracted by the core (C) type of material in the core (D) amount of material in the core
Output:
B