You are given a science question (easy-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 organ is made mostly of muscle?  
 (A) heart (B) lung (C) ear (D) brain

Ex Output:
A


Ex Input:
Many things can contribute to the development of a theory. A student made a list of some things that might help scientists develop a theory. Observations Calculations Conversations Publications From the student's list, which must be used in the development of every theory?  
 (A) Observations (B) Conversations (C) Publications and calculations (D) Calculations and conversations

Ex Output:
A


Ex Input:
Which force causes rocks to roll downhill?  
 (A) gravity (B) friction (C) erosion (D) magnetism

Ex Output:

A