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 Q]: Emily made a cup of tea and stirred it with a spoon. The spoon became warm. How was the heat from the tea transferred to the spoon?  
 (A) convection (B) radiation (C) conduction (D) evaporation
[EX A]: C

[EX Q]: 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 A]: B

[EX Q]: Which of the following best describes the purpose of the chromosomes in the nucleus of a cell?  
 (A) to store the genetic instructions needed to specify traits (B) to release energy by breaking down food molecules (C) to transport nutrients into and out of the cell (D) to protect the cells from microorganisms
[EX A]:
A