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.

Example Input: Surface mining is a type of mining that is done at the surface of Earth. In addition to supplying valuable minerals to industry, surface mining might also
(A) discourage landfills. (B) increase Earth's surface area. (C) eliminate groundwater pollution. (D) create recreational ponds and lakes.
Example Output: D

Example Input: Which of these is an environmental benefit of converting to solar energy?
(A) a decrease in air pollution (B) an increase in the cost of energy (C) an increase in the use of fossil fuels (D) a decrease in electrical energy production
Example Output: A

Example Input: What characteristic of DNA results in cell differentiation in developing embryos?
(A) which genes are present (B) how many copies of each gene are present (C) which genes are active (D) what protein is produced by a gene
Example Output:
C