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 action creates competition between environmental concerns and economic gains?  
 (A) protecting endangered wildlife (B) reintroducing wildlife into their natural habitats (C) using forest land to build homes (D) using city buses for transportation

Output: C


Input: Consider Input: Many horses grow a heavy coat in autumn and shed that coat in spring. Scientists were not sure if temperature or the amount of daylight per day (called the photoperiod) caused the change. So, they conducted an experiment and concluded that the change in photoperiod was responsible for the biological changes. Shedding caused by which set of conditions would have helped them arrive at this conclusion?  
 (A) a constant photoperiod, but varied temperatures (B) a varied photoperiod, and varied temperatures (C) a constant photoperiod, and a constant temperature (D) a varied photoperiod, but a constant temperature

Output: D


Input: Consider Input: During which phase change is heat energy absorbed by a substance?  
 (A) liquid to gas (B) gas to solid (C) liquid to solid (D) gas to liquid


Output: A