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 substance is a compound?  
 (A) butter (B) nitrogen (C) hydrogen (D) ammonia

Output: D


Input: Consider Input: 22 Sandy is conducting an investigation to find out which food his dog likes best. Which is the manipulated variable in his investigation?  
 (A) The color of his dog's food dish (B) The kind of food he gives his dog (C) The amount of food he gives his dog (D) The time of day he feeds his dog

Output: B


Input: Consider Input: A student investigated the effect of iron on the growth of plants. Four identical plants received a different amount of iron supplement when being watered. This investigation could have been improved if there were  
 (A) earthworms in the soil. (B) fewer plants in the experiment. (C) plants that received water without iron supplements. (D) plants that received different amounts of sunlight.


Output: C