TASK DEFINITION: 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.
PROBLEM: 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

SOLUTION: C

PROBLEM: Which term best describes the nature of all light waves?  
 (A) longitudinal (B) transverse (C) compressional (D) magnetic

SOLUTION: B

PROBLEM: Wind is a natural resource that benefits the southeastern shore of the Chesapeake Bay. How could these winds best benefit humans?  
 (A) The winds could blow oil spills into the bay. (B) The winds could be converted to fossil fuel. (C) The winds could blow air pollution toward land. (D) The winds could be converted to electrical energy.

SOLUTION:
D