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.

Ex Input:
Which is a hypothesis that can be easily tested?  
 (A) The Moon causes high tides. (B) During which season are the tides the highest? (C) What is the phase of the Moon when tides are highest? (D) When the Moon is full, the tides will be at their highest.

Ex Output:
D


Ex Input:
Water freezing is an example of a  
 (A) liquid changing to a solid (B) solid changing to a liquid (C) gas changing to a solid (D) gas changing to a liquid

Ex Output:
A


Ex Input:
Scientists conduct investigations to answer questions. Before making a valid conclusion, scientists must  
 (A) collect relevant evidence (B) tell people about the data (C) publish results from the investigation (D) discuss the investigation with other scientists

Ex Output:

A