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:
Researchers recently discovered a gene in humans that previously was unknown to science. Which statement best explains why the gene probably was not discovered much sooner?
(A) The gene only recently evolved in humans. (B) The technology used to study genes is still being developed. (C) Scientists were not interested in genes until a few years ago. (D) Scientists were sure they had already discovered every possible gene.

Ex Output:
B

Ex Input:
A pot is touching the flame of a gas stove, and the substance in the pot is heating up due to the contact. This is an example of which type of energy transfer?
(A) radiation (B) convection (C) conduction (D) vaporization

Ex Output:
C

Ex Input:
Which is a problem with using wind turbines to produce energy?
(A) Wind turbines are efficient only in certain areas. (B) Wind turbines occupy a small area of land. (C) Wind turbines produce a large amount of energy. (D) Wind turbines create a large amount of pollution.

Ex Output:
A