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:
An astronomer is studying two stars that are the same distance from Earth. Star X appears brighter than star Y. Which statement best explains this observation?  
 (A) Star X is larger than star Y. (B) Star Y is larger than star X. (C) Star X reflects the Sun’s light better than star Y. (D) Star Y reflects the Sun’s light better than star X.

Ex Output:
A


Ex Input:
Two forms of boron are naturally occurring, boron-10 and boron-11. What difference exists between a boron atom with a 10 atomic mass units (amu) and a boron atom with 11 atomic mass units (amu)?  
 (A) amount of neutrons (B) number of electrons (C) size of protons and neutrons (D) size of electrons and electron cloud

Ex Output:
A


Ex Input:
Which activity is an example of a chemical change?  
 (A) sugar dissolving in water (B) water evaporating in air (C) lighting a match (D) freezing water

Ex Output:

C